Hi guys, Short sumarry: Wonder if hibernate could get a feature to kind of either unproxy or freeze the entities once leaving the managed context to avoid uncontrolled lazy loading on one side and serialization issues on another side. Use case example: a common example is a REST service exposing directly hibernate entities (which is more and more common with microservice "movement"). Objective: the goal is to not need any step - or reduce them a lot - between the hibernate interaction and a potential serialization to avoid issues with lazy loading and unexpected loading. Today it requires some custom and hibernate specific logic in the serializer which kind of breaks the transversality of the two concerns (serialization and object management/loading). Implementation options I see: 1. a callback requesting if the lazy relationship should be fetched, something like public interface GraphVisitor { boolean shouldLoad(Object rootEntity, Property property); } 2. An utility to remove any proxy potentially throwing an exception and replacing the value by null or an empty collection, something like MyEntity e = Hibernate.deepUnproxy(entity); 3. A switch of the proxy implementation, this is close to 2 but wouldn't require a call to any utility, just a configuration in the persistence unit. Side note: of course all 3 options can be mixed to create a single solution like having 3 implemented based on 1 for instance. Configuration proposal: this would be activated through a property in the persistence unit (this shouldn't be only global IMHO cause otherwise you can't mix 2 kind of units, like one for JSF and one for JAX-RS to be concrete). This should also be activable as a query hint i think - but more a nice to have. What this feature wouldn't be responsible for: cycles. If relationships are bidirectional then the unproxied entity would still "loop" if you browse the object graph - this responsability would stay in the consumer since it doesn't depend on hibernate directly but more on a plain object handling. What do you think? Romain Manni-Bucau @rmannibucau <https://twitter.com/rmannibucau> | Blog <https://blog-rmannibucau.rhcloud.com> | Old Blog <http://rmannibucau.wordpress.com> | Github <https://github.com/rmannibucau> | LinkedIn <https://www.linkedin.com/in/rmannibucau> | JavaEE Factory <https://javaeefactory-rmannibucau.rhcloud.com> _______________________________________________ hibernate-dev mailing list hibernate-dev(a)lists.jboss.org https://lists.jboss.org/mailman/listinfo/hibernate-dev

Hi, Although I keep on seeing this request from time to time, I still think it's more like a Code Smell. Entities are useful for when you plan to modify them. Otherwise, a DTO projection is much more efficient, and you don't suffer from LazyInitializationException. With the ResultTransformer, you can even build graphs of entities, as explained in this article; https://vladmihalcea.com/2017/04/03/why-you-should-use-the-hibernate-resu... Due to how Hibernate Proxies are handled, without Bytecode Enhancement, it's difficult to replace a Proxy with null after the Session is closed. If we implemented this, we'd have to take into consideration both Javassist and ByteBuddy as well as ByteCode Enhancements. all in all, the implementation effort might not justify the benefit, and I'm skeptical of offering a feature that does not encourage data access Best Practices. Vlad On Wed, Apr 19, 2017 at 2:18 PM, Christian Beikov < christian.beikov(a)gmail.com&gt; wrote: > Hey Romain, > > I don't think it is a good idea to expose entities directly if you > really need a subset of the data. > Reasons for that thinking are that it gets hard to define what needs to > be fetched or is safe to be used for a particular use case. Obviously > serialization is like a follow-up problem. > I see 2 possible solutions to the problem and both boil down to the use > of DTOs. > > 1. Use an object mapper(e.g. Dozer) that maps entity object graphs to > custom DTO types. > 2. Use specialized DTOs in queries. > > > Implementing 1. does not help you with lazy loading issues and 2. might > require very intrusive changes in queries which is why I implemented > Blaze-Persistence Entity Views > <https://github.com/beikov/blaze-persistence#entity-view-usage>;. > This is a library that allows you to define DTOs with mappings to the > entity. In a query you can define that you want results to be > "materialized" as instances of the DTO type. > This reduces the pain induced by properly separating the "presentation > model" from the "persistence model" and at the same time will improve > the performance by utilizing the mapping information. > I don't want to advertise too much, just wanted to say that I had the > same issues over and over which is why I started that project. > > Mit freundlichen Grüßen, > ------------------------------------------------------------------------ > *Christian Beikov* > Am 19.04.2017 um 10:51 schrieb Romain Manni-Bucau: > > Hi guys, > > > > Short sumarry: Wonder if hibernate could get a feature to kind of either > > unproxy or freeze the entities once leaving the managed context to avoid > > uncontrolled lazy loading on one side and serialization issues on another > > side. > > > > Use case example: a common example is a REST service exposing directly > > hibernate entities (which is more and more common with microservice > > "movement"). > > > > Objective: the goal is to not need any step - or reduce them a lot - > > between the hibernate interaction and a potential serialization to avoid > > issues with lazy loading and unexpected loading. Today it requires some > > custom and hibernate specific logic in the serializer which kind of > breaks > > the transversality of the two concerns (serialization and object > > management/loading). > > > > > > Implementation options I see: > > > > 1. a callback requesting if the lazy relationship should be fetched, > > something like > > > > public interface GraphVisitor { > > boolean shouldLoad(Object rootEntity, Property property); > > } > > > > 2. An utility to remove any proxy potentially throwing an exception and > > replacing the value by null or an empty collection, something like > > > > MyEntity e = Hibernate.deepUnproxy(entity); > > > > 3. A switch of the proxy implementation, this is close to 2 but wouldn't > > require a call to any utility, just a configuration in the persistence > unit. > > > > Side note: of course all 3 options can be mixed to create a single > solution > > like having 3 implemented based on 1 for instance. > > > > Configuration proposal: this would be activated through a property in the > > persistence unit (this shouldn't be only global IMHO cause otherwise you > > can't mix 2 kind of units, like one for JSF and one for JAX-RS to be > > concrete). This should also be activable as a query hint i think - but > more > > a nice to have. > > > > > > What this feature wouldn't be responsible for: cycles. If relationships > are > > bidirectional then the unproxied entity would still "loop" if you browse > > the object graph - this responsability would stay in the consumer since > it > > doesn't depend on hibernate directly but more on a plain object handling. > > > > What do you think? > > > > > > Romain Manni-Bucau > > @rmannibucau <https://twitter.com/rmannibucau> | Blog > > <https://blog-rmannibucau.rhcloud.com> | Old Blog > > <http://rmannibucau.wordpress.com> | Github <https://github.com/ > rmannibucau> | > > LinkedIn <https://www.linkedin.com/in/rmannibucau> | JavaEE Factory > > <https://javaeefactory-rmannibucau.rhcloud.com> > > _______________________________________________ > > hibernate-dev mailing list > > hibernate-dev(a)lists.jboss.org > > https://lists.jboss.org/mailman/listinfo/hibernate-dev > > _______________________________________________ > hibernate-dev mailing list > hibernate-dev(a)lists.jboss.org > https://lists.jboss.org/mailman/listinfo/hibernate-dev > _______________________________________________ hibernate-dev mailing list hibernate-dev(a)lists.jboss.org https://lists.jboss.org/mailman/listinfo/hibernate-dev

I was very much in the Vlad, Steve, Christian camp until relatively recently. One of my main concern being that replacing a proxy by null was really sending the wrong message. So I was against having Hibernate ORM facilitate such a transformation. I am changing my mind because I am realizing that a lot of applications are less complex that my perceived median. A lot of apps really just want data to be fetched out and then passed to jackson (implicitly) and pushed out as a REST response in JSON or some other serialization protocol. So while we could try and keep the stance that such a solution should remain out of scope of Hibernate ORM core, we should have a very smooth integration with something like MapStruct to create such bounded DTO on the fly. Ideally with as close to zero code as possible from the user point of view. I can't really describe how that could look like because I am not familiar enough with MapStruct but I think it should have the following characteristics: 1. do an implicit binding between the mapped object graph and a detached object graph with a 1-1 mapping of type and replacing lazy objects and collections with null. That's the smoothest approach and the most common use case but also the one where an inexperienced person could shoot at someone else's foot 2. do a binding between the mapped object graph and a detached version of that object graph with a 1-1 mapping of type, but declaratively expressing the boundaries for the detached version. This enforces a clear thinking of the boundaries and will load lazy data in case the object graph loaded is missing a bit. I like the idea on principle but I think it overlaps a lot with the fetch graph. 3. offer a full integration between MapStruct and Hibernate ORM by letting people express a full fledge MapStruct transformation between the managed object graph and a different target structure I favored MapStruct over Dozer because we know the MapStruct lead quite well ;) Note however that the MapStruct approach requires an explicit object copy, it feels a bit sad to have to double memory consumption. But that might be a good enough approach and bypassing the managed object creation leads to questions around the Persistence Context contract where loading an object supposedly means it will be in the PC. Maybe a constructor like query syntax allowing to reference a MapStruct conversion logic might work? select mapStruct('order-and-items', o) from Order o left join fetch o.items Emmanuel On Wed 17-04-19 14:29, Vlad Mihalcea wrote: >Hi, > >Although I keep on seeing this request from time to time, I still think >it's more like a Code Smell. >Entities are useful for when you plan to modify them. Otherwise, a DTO >projection is much more efficient, and you don't suffer from >LazyInitializationException. > >With the ResultTransformer, you can even build graphs of entities, as >explained in this article; > >https://vladmihalcea.com/2017/04/03/why-you-should-use-the-hibernate- resulttransformer-to-customize-result-set-mappings/ > >Due to how Hibernate Proxies are handled, without Bytecode Enhancement, >it's difficult to replace a Proxy with null after the Session is closed. If >we implemented this, we'd have to take into consideration both Javassist >and ByteBuddy as well as ByteCode Enhancements. > >all in all, the implementation effort might not justify the benefit, and >I'm skeptical of offering a feature that does not encourage data access >Best Practices. > >Vlad > >On Wed, Apr 19, 2017 at 2:18 PM, Christian Beikov < &gt;christian.beikov(a)gmail.com&gt; wrote: > >> Hey Romain, >> >> I don't think it is a good idea to expose entities directly if you >> really need a subset of the data. >> Reasons for that thinking are that it gets hard to define what needs to >> be fetched or is safe to be used for a particular use case. Obviously >> serialization is like a follow-up problem. >> I see 2 possible solutions to the problem and both boil down to the use >> of DTOs. >> >> 1. Use an object mapper(e.g. Dozer) that maps entity object graphs to >> custom DTO types. >> 2. Use specialized DTOs in queries. >> >> >> Implementing 1. does not help you with lazy loading issues and 2. might >> require very intrusive changes in queries which is why I implemented >> Blaze-Persistence Entity Views >> <https://github.com/beikov/blaze-persistence#entity-view-usage>;. >> This is a library that allows you to define DTOs with mappings to the >> entity. In a query you can define that you want results to be >> "materialized" as instances of the DTO type. >> This reduces the pain induced by properly separating the "presentation >> model" from the "persistence model" and at the same time will improve >> the performance by utilizing the mapping information. >> I don't want to advertise too much, just wanted to say that I had the >> same issues over and over which is why I started that project. >> >> Mit freundlichen Grüßen, >> ------------------------------------------------------------ ------------ >> *Christian Beikov* >> Am 19.04.2017 um 10:51 schrieb Romain Manni-Bucau: >> > Hi guys, >> > >> > Short sumarry: Wonder if hibernate could get a feature to kind of either >> > unproxy or freeze the entities once leaving the managed context to avoid >> > uncontrolled lazy loading on one side and serialization issues on another >> > side. >> > >> > Use case example: a common example is a REST service exposing directly >> > hibernate entities (which is more and more common with microservice >> > "movement"). >> > >> > Objective: the goal is to not need any step - or reduce them a lot - >> > between the hibernate interaction and a potential serialization to avoid >> > issues with lazy loading and unexpected loading. Today it requires some >> > custom and hibernate specific logic in the serializer which kind of >> breaks >> > the transversality of the two concerns (serialization and object >> > management/loading). >> > >> > >> > Implementation options I see: >> > >> > 1. a callback requesting if the lazy relationship should be fetched, >> > something like >> > >> > public interface GraphVisitor { >> > boolean shouldLoad(Object rootEntity, Property property); >> > } >> > >> > 2. An utility to remove any proxy potentially throwing an exception and >> > replacing the value by null or an empty collection, something like >> > >> > MyEntity e = Hibernate.deepUnproxy(entity); >> > >> > 3. A switch of the proxy implementation, this is close to 2 but wouldn't >> > require a call to any utility, just a configuration in the persistence >> unit. >> > >> > Side note: of course all 3 options can be mixed to create a single >> solution >> > like having 3 implemented based on 1 for instance. >> > >> > Configuration proposal: this would be activated through a property in the >> > persistence unit (this shouldn't be only global IMHO cause otherwise you >> > can't mix 2 kind of units, like one for JSF and one for JAX-RS to be >> > concrete). This should also be activable as a query hint i think - but >> more >> > a nice to have. >> > >> > >> > What this feature wouldn't be responsible for: cycles. If relationships >> are >> > bidirectional then the unproxied entity would still "loop" if you browse >> > the object graph - this responsability would stay in the consumer since >> it >> > doesn't depend on hibernate directly but more on a plain object handling. >> > >> > What do you think? >> > >> > >> > Romain Manni-Bucau >> > @rmannibucau <https://twitter.com/rmannibucau> | Blog >> > <https://blog-rmannibucau.rhcloud.com> | Old Blog >> > <http://rmannibucau.wordpress.com> | Github <https://github.com/ >> rmannibucau> | >> > LinkedIn <https://www.linkedin.com/in/rmannibucau> | JavaEE Factory >> > <https://javaeefactory-rmannibucau.rhcloud.com> >> > _______________________________________________ >> > hibernate-dev mailing list >> > hibernate-dev(a)lists.jboss.org >> > https://lists.jboss.org/mailman/listinfo/hibernate-dev >> >> _______________________________________________ >> hibernate-dev mailing list >> hibernate-dev(a)lists.jboss.org >> https://lists.jboss.org/mailman/listinfo/hibernate-dev >> >_______________________________________________ >hibernate-dev mailing list &gt;hibernate-dev(a)lists.jboss.org >https://lists.jboss.org/mailman/listinfo/hibernate-dev _______________________________________________ hibernate-dev mailing list hibernate-dev(a)lists.jboss.org https://lists.jboss.org/mailman/listinfo/hibernate-dev

Following up a bit on my previous email. While a core integration might be best I think, if there are too much reluctance, we can start with a dedicated hibernate-dto or whatever module or even separate project that makes life easier for these "pass through" use cases. This could be in the form of a wrapper API of sort and hence not affect existing Hibernate ORM APIs. Note that the ResultTransformer approach feels like it goes a long way towards fixing the problem but as demonstrated in Vlad's article https://vladmihalcea.com/2017/04/03/why-you-should-use-the-hibernate-resu... it still requires quite a bit of code and a special DTO constructor object. That's what we need to get rid of I think. Emmanuel On Thu 17-05-04 10:04, Emmanuel Bernard wrote: > I was very much in the Vlad, Steve, Christian camp until relatively > recently. One of my main concern being that replacing a proxy by null > was really sending the wrong message. So I was against having Hibernate > ORM facilitate such a transformation. > > I am changing my mind because I am realizing that a lot of applications > are less complex that my perceived median. A lot of apps really just > want data to be fetched out and then passed to jackson (implicitly) and > pushed out as a REST response in JSON or some other serialization > protocol. > > So while we could try and keep the stance that such a solution should > remain out of scope of Hibernate ORM core, we should have a very smooth > integration with something like MapStruct to create such bounded DTO on > the fly. Ideally with as close to zero code as possible from the user > point of view. > I can't really describe how that could look like because I am not > familiar enough with MapStruct but I think it should have the following > characteristics: > > 1. do an implicit binding between the mapped object graph and a detached > object graph with a 1-1 mapping of type and replacing lazy objects and > collections with null. That's the smoothest approach and the most > common use case but also the one where an inexperienced person could > shoot at someone else's foot > 2. do a binding between the mapped object graph and a detached version of > that object graph with a 1-1 mapping of type, but declaratively > expressing the boundaries for the detached version. This enforces a > clear thinking of the boundaries and will load lazy data in case the > object graph loaded is missing a bit. I like the idea on principle but > I think it overlaps a lot with the fetch graph. > 3. offer a full integration between MapStruct and Hibernate ORM by > letting people express a full fledge MapStruct transformation between > the managed object graph and a different target structure > > I favored MapStruct over Dozer because we know the MapStruct lead quite well ;) > > Note however that the MapStruct approach requires an explicit object > copy, it feels a bit sad to have to double memory consumption. But that > might be a good enough approach and bypassing the managed object > creation leads to questions around the Persistence Context contract > where loading an object supposedly means it will be in the PC. > Maybe a constructor like query syntax allowing to reference a MapStruct > conversion logic might work? > > select mapStruct('order-and-items', o) from Order o left join fetch o.items > > Emmanuel > > > On Wed 17-04-19 14:29, Vlad Mihalcea wrote: >> Hi, >> >> Although I keep on seeing this request from time to time, I still think >> it's more like a Code Smell. >> Entities are useful for when you plan to modify them. Otherwise, a DTO >> projection is much more efficient, and you don't suffer from >> LazyInitializationException. >> >> With the ResultTransformer, you can even build graphs of entities, as >> explained in this article; >> >> https://vladmihalcea.com/2017/04/03/why-you-should-use-the-hibernate-resu... >> >> Due to how Hibernate Proxies are handled, without Bytecode Enhancement, >> it's difficult to replace a Proxy with null after the Session is closed. If >> we implemented this, we'd have to take into consideration both Javassist >> and ByteBuddy as well as ByteCode Enhancements. >> >> all in all, the implementation effort might not justify the benefit, and >> I'm skeptical of offering a feature that does not encourage data access >> Best Practices. >> >> Vlad >> >> On Wed, Apr 19, 2017 at 2:18 PM, Christian Beikov < >> christian.beikov(a)gmail.com&gt; wrote: >> >>> Hey Romain, >>> >>> I don't think it is a good idea to expose entities directly if you >>> really need a subset of the data. >>> Reasons for that thinking are that it gets hard to define what needs to >>> be fetched or is safe to be used for a particular use case. Obviously >>> serialization is like a follow-up problem. >>> I see 2 possible solutions to the problem and both boil down to the use >>> of DTOs. >>> >>> 1. Use an object mapper(e.g. Dozer) that maps entity object graphs to >>> custom DTO types. >>> 2. Use specialized DTOs in queries. >>> >>> >>> Implementing 1. does not help you with lazy loading issues and 2. might >>> require very intrusive changes in queries which is why I implemented >>> Blaze-Persistence Entity Views >>> <https://github.com/beikov/blaze-persistence#entity-view-usage>;. >>> This is a library that allows you to define DTOs with mappings to the >>> entity. In a query you can define that you want results to be >>> "materialized" as instances of the DTO type. >>> This reduces the pain induced by properly separating the "presentation >>> model" from the "persistence model" and at the same time will improve >>> the performance by utilizing the mapping information. >>> I don't want to advertise too much, just wanted to say that I had the >>> same issues over and over which is why I started that project. >>> >>> Mit freundlichen Grüßen, >>> ------------------------------------------------------------------------ >>> *Christian Beikov* >>> Am 19.04.2017 um 10:51 schrieb Romain Manni-Bucau: >>>> Hi guys, >>>> >>>> Short sumarry: Wonder if hibernate could get a feature to kind of either >>>> unproxy or freeze the entities once leaving the managed context to avoid >>>> uncontrolled lazy loading on one side and serialization issues on another >>>> side. >>>> >>>> Use case example: a common example is a REST service exposing directly >>>> hibernate entities (which is more and more common with microservice >>>> "movement"). >>>> >>>> Objective: the goal is to not need any step - or reduce them a lot - >>>> between the hibernate interaction and a potential serialization to avoid >>>> issues with lazy loading and unexpected loading. Today it requires some >>>> custom and hibernate specific logic in the serializer which kind of >>> breaks >>>> the transversality of the two concerns (serialization and object >>>> management/loading). >>>> >>>> >>>> Implementation options I see: >>>> >>>> 1. a callback requesting if the lazy relationship should be fetched, >>>> something like >>>> >>>> public interface GraphVisitor { >>>> boolean shouldLoad(Object rootEntity, Property property); >>>> } >>>> >>>> 2. An utility to remove any proxy potentially throwing an exception and >>>> replacing the value by null or an empty collection, something like >>>> >>>> MyEntity e = Hibernate.deepUnproxy(entity); >>>> >>>> 3. A switch of the proxy implementation, this is close to 2 but wouldn't >>>> require a call to any utility, just a configuration in the persistence >>> unit. >>>> Side note: of course all 3 options can be mixed to create a single >>> solution >>>> like having 3 implemented based on 1 for instance. >>>> >>>> Configuration proposal: this would be activated through a property in the >>>> persistence unit (this shouldn't be only global IMHO cause otherwise you >>>> can't mix 2 kind of units, like one for JSF and one for JAX-RS to be >>>> concrete). This should also be activable as a query hint i think - but >>> more >>>> a nice to have. >>>> >>>> >>>> What this feature wouldn't be responsible for: cycles. If relationships >>> are >>>> bidirectional then the unproxied entity would still "loop" if you browse >>>> the object graph - this responsability would stay in the consumer since >>> it >>>> doesn't depend on hibernate directly but more on a plain object handling. >>>> >>>> What do you think? >>>> >>>> >>>> Romain Manni-Bucau >>>> @rmannibucau <https://twitter.com/rmannibucau> | Blog >>>> <https://blog-rmannibucau.rhcloud.com> | Old Blog >>>> <http://rmannibucau.wordpress.com> | Github <https://github.com/ >>> rmannibucau> | >>>> LinkedIn <https://www.linkedin.com/in/rmannibucau> | JavaEE Factory >>>> <https://javaeefactory-rmannibucau.rhcloud.com> >>>> _______________________________________________ >>>> hibernate-dev mailing list >>>> hibernate-dev(a)lists.jboss.org >>>> https://lists.jboss.org/mailman/listinfo/hibernate-dev >>> _______________________________________________ >>> hibernate-dev mailing list >>> hibernate-dev(a)lists.jboss.org >>> https://lists.jboss.org/mailman/listinfo/hibernate-dev >>> >> _______________________________________________ >> hibernate-dev mailing list >> hibernate-dev(a)lists.jboss.org >> https://lists.jboss.org/mailman/listinfo/hibernate-dev > _______________________________________________ > hibernate-dev mailing list > hibernate-dev(a)lists.jboss.org > https://lists.jboss.org/mailman/listinfo/hibernate-dev _______________________________________________ hibernate-dev mailing list hibernate-dev(a)lists.jboss.org https://lists.jboss.org/mailman/listinfo/hibernate-dev

Were there a standard "represent something in XML-ish format" contract portable across a number of formats (XML, JAXB, JSON, etc) then I'd be more inclined to agree with this. But as it is, supporting this would mean Hibernate implementing multiple such contracts, one per format. However, 1. these formats are not our core competency 2. maintaining a complete set of these transformers across all the popular formats du-jour is a large undertaking 3. I am not convinced that All of these increase the technical risk. Additionally, to properly support this we'd really need the ability to then "map" multiple views for a given entity-graph-root. What I mean by that, is that such DTO approaches often need multiple "views" of a given entity, e.g. a CompanyListDTO, CompanyOverviewDTO, CompanyDetailsGeneralDTO, etc for a Company entity. The point of this is that 1. the transformers for these are specific to each DTO type and would be applied per-transformation 2. were Hibernate to "provide" this for applications IMO the use of queries to obtain views is logical. Populating each of those specific DTOs (CompanyListDTO, etc) in the most efficient way is going to require very different SQL for each DTO. This implies some kind of "mapping" to be able associate each DTO with query. Given 6.0's improved dynamic-instantiation support, I even think that is a great solution as well *for most cases*. So, while my objection has a "practical impact" component, I also just question whether Hibernate integrating with each format's "serializer" is the proper solution. On Thu, May 4, 2017 at 5:08 AM Christian Beikov < christian.beikov(a)gmail.com&gt; wrote: > This is exactly what I am trying to do with Blaze-Persistence Entity > Views, making DTOs sexy and efficient :) > > Here a quick overview of how that looks like right now: > > https://persistence.blazebit.com/documentation/entity-view/manual/en_US/i... > > One of my targets is to make it possible to do something like this > > entityManager.createQuery("FROM Order o", OrderDTO.class).getResultList() > > and get an optimal query, as well as objects with only the necessary > contents. > > Maybe we can collaborate on that somehow? > > > Mit freundlichen Grüßen, > ------------------------------------------------------------------------ > *Christian Beikov* > Am 04.05.2017 um 10:20 schrieb Emmanuel Bernard: > > Following up a bit on my previous email. > > > > While a core integration might be best I think, if there are too much > > reluctance, we can start with a dedicated hibernate-dto or whatever > > module or even separate project that makes life easier for these "pass > > through" use cases. This could be in the form of a wrapper API of sort > > and hence not affect existing Hibernate ORM APIs. > > > > Note that the ResultTransformer approach feels like it goes a long way > > towards fixing the problem but as demonstrated in Vlad's article > > > https://vladmihalcea.com/2017/04/03/why-you-should-use-the-hibernate-resu... > > it still requires quite a bit of code and a special DTO constructor > > object. That's what we need to get rid of I think. > > > > Emmanuel > > > > On Thu 17-05-04 10:04, Emmanuel Bernard wrote: > >> I was very much in the Vlad, Steve, Christian camp until relatively > >> recently. One of my main concern being that replacing a proxy by null > >> was really sending the wrong message. So I was against having Hibernate > >> ORM facilitate such a transformation. > >> > >> I am changing my mind because I am realizing that a lot of applications > >> are less complex that my perceived median. A lot of apps really just > >> want data to be fetched out and then passed to jackson (implicitly) and > >> pushed out as a REST response in JSON or some other serialization > >> protocol. > >> > >> So while we could try and keep the stance that such a solution should > >> remain out of scope of Hibernate ORM core, we should have a very smooth > >> integration with something like MapStruct to create such bounded DTO on > >> the fly. Ideally with as close to zero code as possible from the user > >> point of view. > >> I can't really describe how that could look like because I am not > >> familiar enough with MapStruct but I think it should have the following > >> characteristics: > >> > >> 1. do an implicit binding between the mapped object graph and a > detached > >> object graph with a 1-1 mapping of type and replacing lazy objects > and > >> collections with null. That's the smoothest approach and the most > >> common use case but also the one where an inexperienced person could > >> shoot at someone else's foot > >> 2. do a binding between the mapped object graph and a detached version > of > >> that object graph with a 1-1 mapping of type, but declaratively > >> expressing the boundaries for the detached version. This enforces a > >> clear thinking of the boundaries and will load lazy data in case the > >> object graph loaded is missing a bit. I like the idea on principle > but > >> I think it overlaps a lot with the fetch graph. > >> 3. offer a full integration between MapStruct and Hibernate ORM by > >> letting people express a full fledge MapStruct transformation > between > >> the managed object graph and a different target structure > >> > >> I favored MapStruct over Dozer because we know the MapStruct lead > quite well ;) > >> > >> Note however that the MapStruct approach requires an explicit object > >> copy, it feels a bit sad to have to double memory consumption. But that > >> might be a good enough approach and bypassing the managed object > >> creation leads to questions around the Persistence Context contract > >> where loading an object supposedly means it will be in the PC. > >> Maybe a constructor like query syntax allowing to reference a MapStruct > >> conversion logic might work? > >> > >> select mapStruct('order-and-items', o) from Order o left join > fetch o.items > >> > >> Emmanuel > >> > >> > >> On Wed 17-04-19 14:29, Vlad Mihalcea wrote: > >>> Hi, > >>> > >>> Although I keep on seeing this request from time to time, I still > think > >>> it's more like a Code Smell. > >>> Entities are useful for when you plan to modify them. Otherwise, a DTO > >>> projection is much more efficient, and you don't suffer from > >>> LazyInitializationException. > >>> > >>> With the ResultTransformer, you can even build graphs of entities, as > >>> explained in this article; > >>> > >>> > https://vladmihalcea.com/2017/04/03/why-you-should-use-the-hibernate-resu... > >>> > >>> Due to how Hibernate Proxies are handled, without Bytecode > Enhancement, > >>> it's difficult to replace a Proxy with null after the Session is > closed. If > >>> we implemented this, we'd have to take into consideration both > Javassist > >>> and ByteBuddy as well as ByteCode Enhancements. > >>> > >>> all in all, the implementation effort might not justify the benefit, > and > >>> I'm skeptical of offering a feature that does not encourage data > access > >>> Best Practices. > >>> > >>> Vlad > >>> > >>> On Wed, Apr 19, 2017 at 2:18 PM, Christian Beikov < > >>> christian.beikov(a)gmail.com&gt; wrote: > >>> > >>>> Hey Romain, > >>>> > >>>> I don't think it is a good idea to expose entities directly if you > >>>> really need a subset of the data. > >>>> Reasons for that thinking are that it gets hard to define what needs > to > >>>> be fetched or is safe to be used for a particular use case. Obviously > >>>> serialization is like a follow-up problem. > >>>> I see 2 possible solutions to the problem and both boil down to the > use > >>>> of DTOs. > >>>> > >>>> 1. Use an object mapper(e.g. Dozer) that maps entity object graphs > to > >>>> custom DTO types. > >>>> 2. Use specialized DTOs in queries. > >>>> > >>>> > >>>> Implementing 1. does not help you with lazy loading issues and 2. > might > >>>> require very intrusive changes in queries which is why I implemented > >>>> Blaze-Persistence Entity Views > >>>> <https://github.com/beikov/blaze-persistence#entity-view-usage>;. > >>>> This is a library that allows you to define DTOs with mappings to the > >>>> entity. In a query you can define that you want results to be > >>>> "materialized" as instances of the DTO type. > >>>> This reduces the pain induced by properly separating the > "presentation > >>>> model" from the "persistence model" and at the same time will improve > >>>> the performance by utilizing the mapping information. > >>>> I don't want to advertise too much, just wanted to say that I had the > >>>> same issues over and over which is why I started that project. > >>>> > >>>> Mit freundlichen Grüßen, > >>>> > ------------------------------------------------------------------------ > >>>> *Christian Beikov* > >>>> Am 19.04.2017 um 10:51 schrieb Romain Manni-Bucau: > >>>>> Hi guys, > >>>>> > >>>>> Short sumarry: Wonder if hibernate could get a feature to kind of > either > >>>>> unproxy or freeze the entities once leaving the managed context to > avoid > >>>>> uncontrolled lazy loading on one side and serialization issues on > another > >>>>> side. > >>>>> > >>>>> Use case example: a common example is a REST service exposing > directly > >>>>> hibernate entities (which is more and more common with microservice > >>>>> "movement"). > >>>>> > >>>>> Objective: the goal is to not need any step - or reduce them a lot - > >>>>> between the hibernate interaction and a potential serialization to > avoid > >>>>> issues with lazy loading and unexpected loading. Today it requires > some > >>>>> custom and hibernate specific logic in the serializer which kind of > >>>> breaks > >>>>> the transversality of the two concerns (serialization and object > >>>>> management/loading). > >>>>> > >>>>> > >>>>> Implementation options I see: > >>>>> > >>>>> 1. a callback requesting if the lazy relationship should be fetched, > >>>>> something like > >>>>> > >>>>> public interface GraphVisitor { > >>>>> boolean shouldLoad(Object rootEntity, Property property); > >>>>> } > >>>>> > >>>>> 2. An utility to remove any proxy potentially throwing an exception > and > >>>>> replacing the value by null or an empty collection, something like > >>>>> > >>>>> MyEntity e = Hibernate.deepUnproxy(entity); > >>>>> > >>>>> 3. A switch of the proxy implementation, this is close to 2 but > wouldn't > >>>>> require a call to any utility, just a configuration in the > persistence > >>>> unit. > >>>>> Side note: of course all 3 options can be mixed to create a single > >>>> solution > >>>>> like having 3 implemented based on 1 for instance. > >>>>> > >>>>> Configuration proposal: this would be activated through a property > in the > >>>>> persistence unit (this shouldn't be only global IMHO cause > otherwise you > >>>>> can't mix 2 kind of units, like one for JSF and one for JAX-RS to be > >>>>> concrete). This should also be activable as a query hint i think - > but > >>>> more > >>>>> a nice to have. > >>>>> > >>>>> > >>>>> What this feature wouldn't be responsible for: cycles. If > relationships > >>>> are > >>>>> bidirectional then the unproxied entity would still "loop" if you > browse > >>>>> the object graph - this responsability would stay in the consumer > since > >>>> it > >>>>> doesn't depend on hibernate directly but more on a plain object > handling. > >>>>> > >>>>> What do you think? > >>>>> > >>>>> > >>>>> Romain Manni-Bucau > >>>>> @rmannibucau <https://twitter.com/rmannibucau> | Blog > >>>>> <https://blog-rmannibucau.rhcloud.com> | Old Blog > >>>>> <http://rmannibucau.wordpress.com> | Github <https://github.com/ > >>>> rmannibucau> | > >>>>> LinkedIn <https://www.linkedin.com/in/rmannibucau> | JavaEE Factory > >>>>> <https://javaeefactory-rmannibucau.rhcloud.com> > >>>>> _______________________________________________ > >>>>> hibernate-dev mailing list > >>>>> hibernate-dev(a)lists.jboss.org > >>>>> https://lists.jboss.org/mailman/listinfo/hibernate-dev > >>>> _______________________________________________ > >>>> hibernate-dev mailing list > >>>> hibernate-dev(a)lists.jboss.org > >>>> https://lists.jboss.org/mailman/listinfo/hibernate-dev > >>>> > >>> _______________________________________________ > >>> hibernate-dev mailing list > >>> hibernate-dev(a)lists.jboss.org > >>> https://lists.jboss.org/mailman/listinfo/hibernate-dev > >> _______________________________________________ > >> hibernate-dev mailing list > >> hibernate-dev(a)lists.jboss.org > >> https://lists.jboss.org/mailman/listinfo/hibernate-dev > > _______________________________________________ > > hibernate-dev mailing list > > hibernate-dev(a)lists.jboss.org > > https://lists.jboss.org/mailman/listinfo/hibernate-dev > > _______________________________________________ > hibernate-dev mailing list > hibernate-dev(a)lists.jboss.org > https://lists.jboss.org/mailman/listinfo/hibernate-dev >

Few more points: 1. Dto dont help at any moment - or you put that logic in the conversion and you are back to start 2. Making jaxb/jsonb easy to integrate is the goal IMO. No need to integrate with them but just provide some utility one level further than existing ones Le 4 mai 2017 16:13, "Steve Ebersole" <steve(a)hibernate.org <mailto:steve@hibernate.org>> a écrit : Oops, that (3) in previous reply should have read: 3. supporting each format creates a new "optional" library dependency Overall, I like Christian's approach as a potential generalized approach to this. Basically a combination of 1. a query used to provide the "view source values" 2. some indication of how to map those "source values" to your view model And again, I think 6.0's improved dynamic-instantiation queries are a simple, already-built-in way to achieve that for most cases. But I am open to discussing a way to supply that combination via API if we deem that would be good - although then I'd also question how the current TupleTransformer does not meet that need. On Thu, May 4, 2017 at 8:43 AM Steve Ebersole <steve(a)hibernate.org <mailto:steve@hibernate.org>> wrote: > Were there a standard "represent something in XML-ish format" contract > portable across a number of formats (XML, JAXB, JSON, etc) then I'd be more > inclined to agree with this. But as it is, supporting this would mean > Hibernate implementing multiple such contracts, one per format. However, > > 1. these formats are not our core competency > 2. maintaining a complete set of these transformers across all the > popular formats du-jour is a large undertaking > 3. I am not convinced that > > All of these increase the technical risk. > > Additionally, to properly support this we'd really need the ability to > then "map" multiple views for a given entity-graph-root. What I mean by > that, is that such DTO approaches often need multiple "views" of a given > entity, e.g. a CompanyListDTO, CompanyOverviewDTO, > CompanyDetailsGeneralDTO, etc for a Company entity. The point of this is > that > > 1. the transformers for these are specific to each DTO type and would > be applied per-transformation > 2. were Hibernate to "provide" this for applications > > IMO the use of queries to obtain views is logical. Populating each of > those specific DTOs (CompanyListDTO, etc) in the most efficient way is > going to require very different SQL for each DTO. This implies some kind > of "mapping" to be able associate each DTO with query. > > Given 6.0's improved dynamic-instantiation support, I even think that is a > great solution as well *for most cases*. > > So, while my objection has a "practical impact" component, I also just > question whether Hibernate integrating with each format's "serializer" is > the proper solution. > > > > On Thu, May 4, 2017 at 5:08 AM Christian Beikov < > christian.beikov(a)gmail.com <mailto:christian.beikov@gmail.com>> wrote: > >> This is exactly what I am trying to do with Blaze-Persistence Entity >> Views, making DTOs sexy and efficient :) >> >> Here a quick overview of how that looks like right now: >> >> https://persistence.blazebit.com/documentation/entity-view/manual/en_US/i... <https://persistence.blazebit.com/documentation/entity-view/manual/en_US/i... >> >> One of my targets is to make it possible to do something like this >> >> entityManager.createQuery("FROM Order o", OrderDTO.class).getResultList() >> >> and get an optimal query, as well as objects with only the necessary >> contents. >> >> Maybe we can collaborate on that somehow? >> >> >> Mit freundlichen Grüßen, >> ------------------------------------------------------------------------ >> *Christian Beikov* >> Am 04.05.2017 um 10:20 schrieb Emmanuel Bernard: >> > Following up a bit on my previous email. >> > >> > While a core integration might be best I think, if there are too much >> > reluctance, we can start with a dedicated hibernate-dto or whatever >> > module or even separate project that makes life easier for these "pass >> > through" use cases. This could be in the form of a wrapper API of sort >> > and hence not affect existing Hibernate ORM APIs. >> > >> > Note that the ResultTransformer approach feels like it goes a long way >> > towards fixing the problem but as demonstrated in Vlad's article >> > >> https://vladmihalcea.com/2017/04/03/why-you-should-use-the-hibernate-resu... <https://vladmihalcea.com/2017/04/03/why-you-should-use-the-hibernate-resu... >> > it still requires quite a bit of code and a special DTO constructor >> > object. That's what we need to get rid of I think. >> > >> > Emmanuel >> > >> > On Thu 17-05-04 10:04, Emmanuel Bernard wrote: >> >> I was very much in the Vlad, Steve, Christian camp until relatively >> >> recently. One of my main concern being that replacing a proxy by null >> >> was really sending the wrong message. So I was against having Hibernate >> >> ORM facilitate such a transformation. >> >> >> >> I am changing my mind because I am realizing that a lot of applications >> >> are less complex that my perceived median. A lot of apps really just >> >> want data to be fetched out and then passed to jackson (implicitly) and >> >> pushed out as a REST response in JSON or some other serialization >> >> protocol. >> >> >> >> So while we could try and keep the stance that such a solution should >> >> remain out of scope of Hibernate ORM core, we should have a very smooth >> >> integration with something like MapStruct to create such bounded DTO on >> >> the fly. Ideally with as close to zero code as possible from the user >> >> point of view. >> >> I can't really describe how that could look like because I am not >> >> familiar enough with MapStruct but I think it should have the following >> >> characteristics: >> >> >> >> 1. do an implicit binding between the mapped object graph and a >> detached >> >> object graph with a 1-1 mapping of type and replacing lazy objects >> and >> >> collections with null. That's the smoothest approach and the most >> >> common use case but also the one where an inexperienced person could >> >> shoot at someone else's foot >> >> 2. do a binding between the mapped object graph and a detached version >> of >> >> that object graph with a 1-1 mapping of type, but declaratively >> >> expressing the boundaries for the detached version. This enforces a >> >> clear thinking of the boundaries and will load lazy data in case the >> >> object graph loaded is missing a bit. I like the idea on principle >> but >> >> I think it overlaps a lot with the fetch graph. >> >> 3. offer a full integration between MapStruct and Hibernate ORM by >> >> letting people express a full fledge MapStruct transformation >> between >> >> the managed object graph and a different target structure >> >> >> >> I favored MapStruct over Dozer because we know the MapStruct lead >> quite well ;) >> >> >> >> Note however that the MapStruct approach requires an explicit object >> >> copy, it feels a bit sad to have to double memory consumption. But that >> >> might be a good enough approach and bypassing the managed object >> >> creation leads to questions around the Persistence Context contract >> >> where loading an object supposedly means it will be in the PC. >> >> Maybe a constructor like query syntax allowing to reference a MapStruct >> >> conversion logic might work? >> >> >> >> select mapStruct('order-and-items', o) from Order o left join >> fetch o.items >> >> >> >> Emmanuel >> >> >> >> >> >> On Wed 17-04-19 14:29, Vlad Mihalcea wrote: >> >>> Hi, >> >>> >> >>> Although I keep on seeing this request from time to time, I still >> think >> >>> it's more like a Code Smell. >> >>> Entities are useful for when you plan to modify them. Otherwise, a DTO >> >>> projection is much more efficient, and you don't suffer from >> >>> LazyInitializationException. >> >>> >> >>> With the ResultTransformer, you can even build graphs of entities, as >> >>> explained in this article; >> >>> >> >>> >> https://vladmihalcea.com/2017/04/03/why-you-should-use-the-hibernate-resu... <https://vladmihalcea.com/2017/04/03/why-you-should-use-the-hibernate-resu... >> >>> >> >>> Due to how Hibernate Proxies are handled, without Bytecode >> Enhancement, >> >>> it's difficult to replace a Proxy with null after the Session is >> closed. If >> >>> we implemented this, we'd have to take into consideration both >> Javassist >> >>> and ByteBuddy as well as ByteCode Enhancements. >> >>> >> >>> all in all, the implementation effort might not justify the benefit, >> and >> >>> I'm skeptical of offering a feature that does not encourage data >> access >> >>> Best Practices. >> >>> >> >>> Vlad >> >>> >> >>> On Wed, Apr 19, 2017 at 2:18 PM, Christian Beikov < >> >>> christian.beikov(a)gmail.com <mailto:christian.beikov@gmail.com>> wrote: >> >>> >> >>>> Hey Romain, >> >>>> >> >>>> I don't think it is a good idea to expose entities directly if you >> >>>> really need a subset of the data. >> >>>> Reasons for that thinking are that it gets hard to define what needs >> to >> >>>> be fetched or is safe to be used for a particular use case. Obviously >> >>>> serialization is like a follow-up problem. >> >>>> I see 2 possible solutions to the problem and both boil down to the >> use >> >>>> of DTOs. >> >>>> >> >>>> 1. Use an object mapper(e.g. Dozer) that maps entity object graphs >> to >> >>>> custom DTO types. >> >>>> 2. Use specialized DTOs in queries. >> >>>> >> >>>> >> >>>> Implementing 1. does not help you with lazy loading issues and 2. >> might >> >>>> require very intrusive changes in queries which is why I implemented >> >>>> Blaze-Persistence Entity Views >> >>>> <https://github.com/beikov/blaze-persistence#entity-view-usage <https://github.com/beikov/blaze-persistence#entity-view-usage>>;. >> >>>> This is a library that allows you to define DTOs with mappings to the >> >>>> entity. In a query you can define that you want results to be >> >>>> "materialized" as instances of the DTO type. >> >>>> This reduces the pain induced by properly separating the >> "presentation >> >>>> model" from the "persistence model" and at the same time will improve >> >>>> the performance by utilizing the mapping information. >> >>>> I don't want to advertise too much, just wanted to say that I had the >> >>>> same issues over and over which is why I started that project. >> >>>> >> >>>> Mit freundlichen Grüßen, >> >>>> >> ------------------------------------------------------------------------ >> >>>> *Christian Beikov* >> >>>> Am 19.04.2017 um 10:51 schrieb Romain Manni-Bucau: >> >>>>> Hi guys, >> >>>>> >> >>>>> Short sumarry: Wonder if hibernate could get a feature to kind of >> either >> >>>>> unproxy or freeze the entities once leaving the managed context to >> avoid >> >>>>> uncontrolled lazy loading on one side and serialization issues on >> another >> >>>>> side. >> >>>>> >> >>>>> Use case example: a common example is a REST service exposing >> directly >> >>>>> hibernate entities (which is more and more common with microservice >> >>>>> "movement"). >> >>>>> >> >>>>> Objective: the goal is to not need any step - or reduce them a lot - >> >>>>> between the hibernate interaction and a potential serialization to >> avoid >> >>>>> issues with lazy loading and unexpected loading. Today it requires >> some >> >>>>> custom and hibernate specific logic in the serializer which kind of >> >>>> breaks >> >>>>> the transversality of the two concerns (serialization and object >> >>>>> management/loading). >> >>>>> >> >>>>> >> >>>>> Implementation options I see: >> >>>>> >> >>>>> 1. a callback requesting if the lazy relationship should be fetched, >> >>>>> something like >> >>>>> >> >>>>> public interface GraphVisitor { >> >>>>> boolean shouldLoad(Object rootEntity, Property property); >> >>>>> } >> >>>>> >> >>>>> 2. An utility to remove any proxy potentially throwing an exception >> and >> >>>>> replacing the value by null or an empty collection, something like >> >>>>> >> >>>>> MyEntity e = Hibernate.deepUnproxy(entity); >> >>>>> >> >>>>> 3. A switch of the proxy implementation, this is close to 2 but >> wouldn't >> >>>>> require a call to any utility, just a configuration in the >> persistence >> >>>> unit. >> >>>>> Side note: of course all 3 options can be mixed to create a single >> >>>> solution >> >>>>> like having 3 implemented based on 1 for instance. >> >>>>> >> >>>>> Configuration proposal: this would be activated through a property >> in the >> >>>>> persistence unit (this shouldn't be only global IMHO cause >> otherwise you >> >>>>> can't mix 2 kind of units, like one for JSF and one for JAX-RS to be >> >>>>> concrete). This should also be activable as a query hint i think - >> but >> >>>> more >> >>>>> a nice to have. >> >>>>> >> >>>>> >> >>>>> What this feature wouldn't be responsible for: cycles. If >> relationships >> >>>> are >> >>>>> bidirectional then the unproxied entity would still "loop" if you >> browse >> >>>>> the object graph - this responsability would stay in the consumer >> since >> >>>> it >> >>>>> doesn't depend on hibernate directly but more on a plain object >> handling. >> >>>>> >> >>>>> What do you think? >> >>>>> >> >>>>> >> >>>>> Romain Manni-Bucau >> >>>>> @rmannibucau <https://twitter.com/rmannibucau <https://twitter.com/rmannibucau>> | Blog >> >>>>> <https://blog-rmannibucau.rhcloud.com <https://blog-rmannibucau.rhcloud.com>> | Old Blog >> >>>>> <http://rmannibucau.wordpress.com <http://rmannibucau.wordpress.com>> | Github <https://github.com/ >> >>>> rmannibucau> | >> >>>>> LinkedIn <https://www.linkedin.com/in/rmannibucau <https://www.linkedin.com/in/rmannibucau>> | JavaEE Factory >> >>>>> <https://javaeefactory-rmannibucau.rhcloud.com <https://javaeefactory-rmannibucau.rhcloud.com>> >> >>>>> _______________________________________________ >> >>>>> hibernate-dev mailing list >> >>>>> hibernate-dev(a)lists.jboss.org <mailto:hibernate-dev@lists.jboss.org> >> >>>>> https://lists.jboss.org/mailman/listinfo/hibernate-dev <https://lists.jboss.org/mailman/listinfo/hibernate-dev> >> >>>> _______________________________________________ >> >>>> hibernate-dev mailing list >> >>>> hibernate-dev(a)lists.jboss.org <mailto:hibernate-dev@lists.jboss.org> >> >>>> https://lists.jboss.org/mailman/listinfo/hibernate-dev <https://lists.jboss.org/mailman/listinfo/hibernate-dev> >> >>>> >> >>> _______________________________________________ >> >>> hibernate-dev mailing list >> >>> hibernate-dev(a)lists.jboss.org <mailto:hibernate-dev@lists.jboss.org> >> >>> https://lists.jboss.org/mailman/listinfo/hibernate-dev <https://lists.jboss.org/mailman/listinfo/hibernate-dev> >> >> _______________________________________________ >> >> hibernate-dev mailing list >> >> hibernate-dev(a)lists.jboss.org <mailto:hibernate-dev@lists.jboss.org> >> >> https://lists.jboss.org/mailman/listinfo/hibernate-dev <https://lists.jboss.org/mailman/listinfo/hibernate-dev> >> > _______________________________________________ >> > hibernate-dev mailing list >> > hibernate-dev(a)lists.jboss.org <mailto:hibernate-dev@lists.jboss.org> >> > https://lists.jboss.org/mailman/listinfo/hibernate-dev <https://lists.jboss.org/mailman/listinfo/hibernate-dev> >> >> _______________________________________________ >> hibernate-dev mailing list >> hibernate-dev(a)lists.jboss.org <mailto:hibernate-dev@lists.jboss.org> >> https://lists.jboss.org/mailman/listinfo/hibernate-dev <https://lists.jboss.org/mailman/listinfo/hibernate-dev> >> > _______________________________________________ hibernate-dev mailing list hibernate-dev(a)lists.jboss.org <mailto:hibernate-dev@lists.jboss.org> https://lists.jboss.org/mailman/listinfo/hibernate-dev <https://lists.jboss.org/mailman/listinfo/hibernate-dev>

Sure. If you add any conversion logic then you are clearly out of hibernate scope and the problem doesnt appear anymore. Here is a trivial example (hopefully trivial at least ;)) User 1 - n Group In json we would get something like {username:...,groups:[group1, group2]}, no issue to know if group should be loaded or not since this part of the logic is in the mapper layer. So yes you can say "not my problem" but next framework will immediately ask "how do i know" and you likely end like all spring-data-rest recommandation with a specific mapping and not a framework solution which is the target of that thread - at least what I tried to explain ;). 2017-05-04 16:41 GMT+02:00 Christian Beikov <christian.beikov(a)gmail.com <mailto:christian.beikov@gmail.com>>: I don't understand what you mean by "you put that logic in the conversion", could you elaborate? Mit freundlichen Grüßen, ------------------------------------------------------------------------ *Christian Beikov* Am 04.05.2017 um 16:32 schrieb Romain Manni-Bucau: > Few more points: > > 1. Dto dont help at any moment - or you put that logic in the > conversion and you are back to start > 2. Making jaxb/jsonb easy to integrate is the goal IMO. No need > to integrate with them but just provide some utility one level > further than existing ones > > Le 4 mai 2017 16:13, "Steve Ebersole" <steve(a)hibernate.org > <mailto:steve@hibernate.org>> a écrit : > > Oops, that (3) in previous reply should have read: > 3. supporting each format creates a new "optional" library > dependency > > Overall, I like Christian's approach as a potential > generalized approach to > this. Basically a combination of > > 1. a query used to provide the "view source values" > 2. some indication of how to map those "source values" to > your view model > > > And again, I think 6.0's improved dynamic-instantiation > queries are a > simple, already-built-in way to achieve that for most cases. > But I am open > to discussing a way to supply that combination via API if we > deem that > would be good - although then I'd also question how the current > TupleTransformer does not meet that need. > > On Thu, May 4, 2017 at 8:43 AM Steve Ebersole > <steve(a)hibernate.org <mailto:steve@hibernate.org>> wrote: > > > Were there a standard "represent something in XML-ish > format" contract > > portable across a number of formats (XML, JAXB, JSON, etc) > then I'd be more > > inclined to agree with this. But as it is, supporting this > would mean > > Hibernate implementing multiple such contracts, one per > format. However, > > > > 1. these formats are not our core competency > > 2. maintaining a complete set of these transformers > across all the > > popular formats du-jour is a large undertaking > > 3. I am not convinced that > > > > All of these increase the technical risk. > > > > Additionally, to properly support this we'd really need the > ability to > > then "map" multiple views for a given entity-graph-root. > What I mean by > > that, is that such DTO approaches often need multiple > "views" of a given > > entity, e.g. a CompanyListDTO, CompanyOverviewDTO, > > CompanyDetailsGeneralDTO, etc for a Company entity. The > point of this is > > that > > > > 1. the transformers for these are specific to each DTO > type and would > > be applied per-transformation > > 2. were Hibernate to "provide" this for applications > > > > IMO the use of queries to obtain views is logical. > Populating each of > > those specific DTOs (CompanyListDTO, etc) in the most > efficient way is > > going to require very different SQL for each DTO. This > implies some kind > > of "mapping" to be able associate each DTO with query. > > > > Given 6.0's improved dynamic-instantiation support, I even > think that is a > > great solution as well *for most cases*. > > > > So, while my objection has a "practical impact" component, > I also just > > question whether Hibernate integrating with each format's > "serializer" is > > the proper solution. > > > > > > > > On Thu, May 4, 2017 at 5:08 AM Christian Beikov < > > christian.beikov(a)gmail.com > <mailto:christian.beikov@gmail.com>> wrote: > > > >> This is exactly what I am trying to do with > Blaze-Persistence Entity > >> Views, making DTOs sexy and efficient :) > >> > >> Here a quick overview of how that looks like right now: > >> > >> > https://persistence.blazebit.com/documentation/entity-view/manual/en_US/i... > <https://persistence.blazebit.com/documentation/entity-view/manual/en_US/i... > >> > >> One of my targets is to make it possible to do something > like this > >> > >> entityManager.createQuery("FROM Order o", > OrderDTO.class).getResultList() > >> > >> and get an optimal query, as well as objects with only the > necessary > >> contents. > >> > >> Maybe we can collaborate on that somehow? > >> > >> > >> Mit freundlichen Grüßen, > >> > ------------------------------------------------------------------------ > >> *Christian Beikov* > >> Am 04.05.2017 um 10:20 schrieb Emmanuel Bernard: > >> > Following up a bit on my previous email. > >> > > >> > While a core integration might be best I think, if there > are too much > >> > reluctance, we can start with a dedicated hibernate-dto > or whatever > >> > module or even separate project that makes life easier > for these "pass > >> > through" use cases. This could be in the form of a > wrapper API of sort > >> > and hence not affect existing Hibernate ORM APIs. > >> > > >> > Note that the ResultTransformer approach feels like it > goes a long way > >> > towards fixing the problem but as demonstrated in Vlad's > article > >> > > >> > https://vladmihalcea.com/2017/04/03/why-you-should-use-the-hibernate-resu... > <https://vladmihalcea.com/2017/04/03/why-you-should-use-the-hibernate-resu... > >> > it still requires quite a bit of code and a special DTO > constructor > >> > object. That's what we need to get rid of I think. > >> > > >> > Emmanuel > >> > > >> > On Thu 17-05-04 10:04, Emmanuel Bernard wrote: > >> >> I was very much in the Vlad, Steve, Christian camp > until relatively > >> >> recently. One of my main concern being that replacing a > proxy by null > >> >> was really sending the wrong message. So I was against > having Hibernate > >> >> ORM facilitate such a transformation. > >> >> > >> >> I am changing my mind because I am realizing that a lot > of applications > >> >> are less complex that my perceived median. A lot of > apps really just > >> >> want data to be fetched out and then passed to jackson > (implicitly) and > >> >> pushed out as a REST response in JSON or some other > serialization > >> >> protocol. > >> >> > >> >> So while we could try and keep the stance that such a > solution should > >> >> remain out of scope of Hibernate ORM core, we should > have a very smooth > >> >> integration with something like MapStruct to create > such bounded DTO on > >> >> the fly. Ideally with as close to zero code as possible > from the user > >> >> point of view. > >> >> I can't really describe how that could look like > because I am not > >> >> familiar enough with MapStruct but I think it should > have the following > >> >> characteristics: > >> >> > >> >> 1. do an implicit binding between the mapped object > graph and a > >> detached > >> >> object graph with a 1-1 mapping of type and > replacing lazy objects > >> and > >> >> collections with null. That's the smoothest approach > and the most > >> >> common use case but also the one where an > inexperienced person could > >> >> shoot at someone else's foot > >> >> 2. do a binding between the mapped object graph and a > detached version > >> of > >> >> that object graph with a 1-1 mapping of type, but > declaratively > >> >> expressing the boundaries for the detached version. > This enforces a > >> >> clear thinking of the boundaries and will load lazy > data in case the > >> >> object graph loaded is missing a bit. I like the > idea on principle > >> but > >> >> I think it overlaps a lot with the fetch graph. > >> >> 3. offer a full integration between MapStruct and > Hibernate ORM by > >> >> letting people express a full fledge MapStruct > transformation > >> between > >> >> the managed object graph and a different target > structure > >> >> > >> >> I favored MapStruct over Dozer because we know the > MapStruct lead > >> quite well ;) > >> >> > >> >> Note however that the MapStruct approach requires an > explicit object > >> >> copy, it feels a bit sad to have to double memory > consumption. But that > >> >> might be a good enough approach and bypassing the > managed object > >> >> creation leads to questions around the Persistence > Context contract > >> >> where loading an object supposedly means it will be in > the PC. > >> >> Maybe a constructor like query syntax allowing to > reference a MapStruct > >> >> conversion logic might work? > >> >> > >> >> select mapStruct('order-and-items', o) from Order o > left join > >> fetch o.items > >> >> > >> >> Emmanuel > >> >> > >> >> > >> >> On Wed 17-04-19 14:29, Vlad Mihalcea wrote: > >> >>> Hi, > >> >>> > >> >>> Although I keep on seeing this request from time to > time, I still > >> think > >> >>> it's more like a Code Smell. > >> >>> Entities are useful for when you plan to modify them. > Otherwise, a DTO > >> >>> projection is much more efficient, and you don't > suffer from > >> >>> LazyInitializationException. > >> >>> > >> >>> With the ResultTransformer, you can even build graphs > of entities, as > >> >>> explained in this article; > >> >>> > >> >>> > >> > https://vladmihalcea.com/2017/04/03/why-you-should-use-the-hibernate-resu... > <https://vladmihalcea.com/2017/04/03/why-you-should-use-the-hibernate-resu... > >> >>> > >> >>> Due to how Hibernate Proxies are handled, without Bytecode > >> Enhancement, > >> >>> it's difficult to replace a Proxy with null after the > Session is > >> closed. If > >> >>> we implemented this, we'd have to take into > consideration both > >> Javassist > >> >>> and ByteBuddy as well as ByteCode Enhancements. > >> >>> > >> >>> all in all, the implementation effort might not > justify the benefit, > >> and > >> >>> I'm skeptical of offering a feature that does not > encourage data > >> access > >> >>> Best Practices. > >> >>> > >> >>> Vlad > >> >>> > >> >>> On Wed, Apr 19, 2017 at 2:18 PM, Christian Beikov < > >> >>> christian.beikov(a)gmail.com > <mailto:christian.beikov@gmail.com>> wrote: > >> >>> > >> >>>> Hey Romain, > >> >>>> > >> >>>> I don't think it is a good idea to expose entities > directly if you > >> >>>> really need a subset of the data. > >> >>>> Reasons for that thinking are that it gets hard to > define what needs > >> to > >> >>>> be fetched or is safe to be used for a particular use > case. Obviously > >> >>>> serialization is like a follow-up problem. > >> >>>> I see 2 possible solutions to the problem and both > boil down to the > >> use > >> >>>> of DTOs. > >> >>>> > >> >>>> 1. Use an object mapper(e.g. Dozer) that maps > entity object graphs > >> to > >> >>>> custom DTO types. > >> >>>> 2. Use specialized DTOs in queries. > >> >>>> > >> >>>> > >> >>>> Implementing 1. does not help you with lazy loading > issues and 2. > >> might > >> >>>> require very intrusive changes in queries which is > why I implemented > >> >>>> Blaze-Persistence Entity Views > >> >>>> > <https://github.com/beikov/blaze-persistence#entity-view-usage > <https://github.com/beikov/blaze-persistence#entity-view-usage>>;. > >> >>>> This is a library that allows you to define DTOs with > mappings to the > >> >>>> entity. In a query you can define that you want > results to be > >> >>>> "materialized" as instances of the DTO type. > >> >>>> This reduces the pain induced by properly separating the > >> "presentation > >> >>>> model" from the "persistence model" and at the same > time will improve > >> >>>> the performance by utilizing the mapping information. > >> >>>> I don't want to advertise too much, just wanted to > say that I had the > >> >>>> same issues over and over which is why I started that > project. > >> >>>> > >> >>>> Mit freundlichen Grüßen, > >> >>>> > >> > ------------------------------------------------------------------------ > >> >>>> *Christian Beikov* > >> >>>> Am 19.04.2017 um 10:51 schrieb Romain Manni-Bucau: > >> >>>>> Hi guys, > >> >>>>> > >> >>>>> Short sumarry: Wonder if hibernate could get a > feature to kind of > >> either > >> >>>>> unproxy or freeze the entities once leaving the > managed context to > >> avoid > >> >>>>> uncontrolled lazy loading on one side and > serialization issues on > >> another > >> >>>>> side. > >> >>>>> > >> >>>>> Use case example: a common example is a REST service > exposing > >> directly > >> >>>>> hibernate entities (which is more and more common > with microservice > >> >>>>> "movement"). > >> >>>>> > >> >>>>> Objective: the goal is to not need any step - or > reduce them a lot - > >> >>>>> between the hibernate interaction and a potential > serialization to > >> avoid > >> >>>>> issues with lazy loading and unexpected loading. > Today it requires > >> some > >> >>>>> custom and hibernate specific logic in the > serializer which kind of > >> >>>> breaks > >> >>>>> the transversality of the two concerns > (serialization and object > >> >>>>> management/loading). > >> >>>>> > >> >>>>> > >> >>>>> Implementation options I see: > >> >>>>> > >> >>>>> 1. a callback requesting if the lazy relationship > should be fetched, > >> >>>>> something like > >> >>>>> > >> >>>>> public interface GraphVisitor { > >> >>>>> boolean shouldLoad(Object rootEntity, Property > property); > >> >>>>> } > >> >>>>> > >> >>>>> 2. An utility to remove any proxy potentially > throwing an exception > >> and > >> >>>>> replacing the value by null or an empty collection, > something like > >> >>>>> > >> >>>>> MyEntity e = Hibernate.deepUnproxy(entity); > >> >>>>> > >> >>>>> 3. A switch of the proxy implementation, this is > close to 2 but > >> wouldn't > >> >>>>> require a call to any utility, just a configuration > in the > >> persistence > >> >>>> unit. > >> >>>>> Side note: of course all 3 options can be mixed to > create a single > >> >>>> solution > >> >>>>> like having 3 implemented based on 1 for instance. > >> >>>>> > >> >>>>> Configuration proposal: this would be activated > through a property > >> in the > >> >>>>> persistence unit (this shouldn't be only global IMHO > cause > >> otherwise you > >> >>>>> can't mix 2 kind of units, like one for JSF and one > for JAX-RS to be > >> >>>>> concrete). This should also be activable as a query > hint i think - > >> but > >> >>>> more > >> >>>>> a nice to have. > >> >>>>> > >> >>>>> > >> >>>>> What this feature wouldn't be responsible for: > cycles. If > >> relationships > >> >>>> are > >> >>>>> bidirectional then the unproxied entity would still > "loop" if you > >> browse > >> >>>>> the object graph - this responsability would stay in > the consumer > >> since > >> >>>> it > >> >>>>> doesn't depend on hibernate directly but more on a > plain object > >> handling. > >> >>>>> > >> >>>>> What do you think? > >> >>>>> > >> >>>>> > >> >>>>> Romain Manni-Bucau > >> >>>>> @rmannibucau <https://twitter.com/rmannibucau > <https://twitter.com/rmannibucau>> | Blog > >> >>>>> <https://blog-rmannibucau.rhcloud.com > <https://blog-rmannibucau.rhcloud.com>> | Old Blog > >> >>>>> <http://rmannibucau.wordpress.com > <http://rmannibucau.wordpress.com>> | Github <https://github.com/ > >> >>>> rmannibucau> | > >> >>>>> LinkedIn <https://www.linkedin.com/in/rmannibucau > <https://www.linkedin.com/in/rmannibucau>> | JavaEE Factory > >> >>>>> <https://javaeefactory-rmannibucau.rhcloud.com > <https://javaeefactory-rmannibucau.rhcloud.com>> > >> >>>>> _______________________________________________ > >> >>>>> hibernate-dev mailing list > >> >>>>> hibernate-dev(a)lists.jboss.org > <mailto:hibernate-dev@lists.jboss.org> > >> >>>>> > https://lists.jboss.org/mailman/listinfo/hibernate-dev > <https://lists.jboss.org/mailman/listinfo/hibernate-dev> > >> >>>> _______________________________________________ > >> >>>> hibernate-dev mailing list > >> >>>> hibernate-dev(a)lists.jboss.org > <mailto:hibernate-dev@lists.jboss.org> > >> >>>> > https://lists.jboss.org/mailman/listinfo/hibernate-dev > <https://lists.jboss.org/mailman/listinfo/hibernate-dev> > >> >>>> > >> >>> _______________________________________________ > >> >>> hibernate-dev mailing list > >> >>> hibernate-dev(a)lists.jboss.org > <mailto:hibernate-dev@lists.jboss.org> > >> >>> https://lists.jboss.org/mailman/listinfo/hibernate-dev > <https://lists.jboss.org/mailman/listinfo/hibernate-dev> > >> >> _______________________________________________ > >> >> hibernate-dev mailing list > >> >> hibernate-dev(a)lists.jboss.org > <mailto:hibernate-dev@lists.jboss.org> > >> >> https://lists.jboss.org/mailman/listinfo/hibernate-dev > <https://lists.jboss.org/mailman/listinfo/hibernate-dev> > >> > _______________________________________________ > >> > hibernate-dev mailing list > >> > hibernate-dev(a)lists.jboss.org > <mailto:hibernate-dev@lists.jboss.org> > >> > https://lists.jboss.org/mailman/listinfo/hibernate-dev > <https://lists.jboss.org/mailman/listinfo/hibernate-dev> > >> > >> _______________________________________________ > >> hibernate-dev mailing list > >> hibernate-dev(a)lists.jboss.org > <mailto:hibernate-dev@lists.jboss.org> > >> https://lists.jboss.org/mailman/listinfo/hibernate-dev > <https://lists.jboss.org/mailman/listinfo/hibernate-dev> > >> > > > _______________________________________________ > hibernate-dev mailing list > hibernate-dev(a)lists.jboss.org > <mailto:hibernate-dev@lists.jboss.org> > https://lists.jboss.org/mailman/listinfo/hibernate-dev > <https://lists.jboss.org/mailman/listinfo/hibernate-dev> >

What exactly would this "utility one level further than existing ones" do?

And for what it is worth, IMO the new Navigable model in 6.0 will again help here. Especially in conjunction with the Navigable visitation support.

On Thu, May 4, 2017 at 10:27 AM Christian Beikov < christian.beikov(a)gmail.com&gt; wrote: > Well that is again exactly what a DTO is good for. If you as developer > want the groups to be available, you add a list of groups to that > special DTO type for that use case. In your data access layer you > somehow populate that, which is normally done by using some mapper > library like MapStruct or Dozer and then JAXB/JSONB can just work with > the DTO type without any problems. > > Now if you forget to add a JOIN FETCH to your query and you end up with > N+1 queries, that's a different problem, just like the amount of > boilerplate code needed for having DTO types for every use case. That I > try to solve with Blaze-Persistence Entity Views. > > Just a quick example to make my point here. If you have a REST endpoint > /user/{id} and want to provide the list of group names along with the > user information, you'd create a UserInfoDTO. > > @EntityView(User.class) > interface UserInfoDTO { > String getUsername(); > @Mapping("groups.name") > List<String> getGroups(); > } > > Your repository returns an object of that type and you just pass that > object through so JAXB/JSONB can do their work. The mapping information > in the DTO is applied on a "source query" i.e. only doing the work > absolutely necessary to satisfy the requested projection. > > Implementing this by hand is by no means impossible, but rather > inconvenient I'd say, which is probably why you are seeking for other > solutions. > > In the end, you can only try to create a minimal DTO that has exactly > the fields you want to be serialized or annotate your existing entities > with those "ignore" annotations and hope for the best. I don't see how > hibernate could or should help in any of the two cases. > > Mit freundlichen Grüßen, > ------------------------------------------------------------------------ > *Christian Beikov* > Am 04.05.2017 um 16:59 schrieb Romain Manni-Bucau: > > Sure. If you add any conversion logic then you are clearly out of > > hibernate scope and the problem doesnt appear anymore. Here is a > > trivial example (hopefully trivial at least ;)) > > > > User 1 - n Group > > > > In json we would get something like {username:...,groups:[group1, > > group2]}, no issue to know if group should be loaded or not since this > > part of the logic is in the mapper layer. > > > > So yes you can say "not my problem" but next framework will > > immediately ask "how do i know" and you likely end like all > > spring-data-rest recommandation with a specific mapping and not a > > framework solution which is the target of that thread - at least what > > I tried to explain ;). > > > > 2017-05-04 16:41 GMT+02:00 Christian Beikov > > <christian.beikov(a)gmail.com <mailto:christian.beikov@gmail.com>>: > > > > I don't understand what you mean by "you put that logic in the > > conversion", could you elaborate? > > > > > > Mit freundlichen Grüßen, > > > ------------------------------------------------------------ ------------ > > *Christian Beikov* > > Am 04.05.2017 um 16:32 schrieb Romain Manni-Bucau: > >> Few more points: > >> > >> 1. Dto dont help at any moment - or you put that logic in the > >> conversion and you are back to start > >> 2. Making jaxb/jsonb easy to integrate is the goal IMO. No need > >> to integrate with them but just provide some utility one level > >> further than existing ones > >> > >> Le 4 mai 2017 16:13, "Steve Ebersole" <steve(a)hibernate.org > >> <mailto:steve@hibernate.org>> a écrit : > >> > >> Oops, that (3) in previous reply should have read: > >> 3. supporting each format creates a new "optional" library > >> dependency > >> > >> Overall, I like Christian's approach as a potential > >> generalized approach to > >> this. Basically a combination of > >> > >> 1. a query used to provide the "view source values" > >> 2. some indication of how to map those "source values" to > >> your view model > >> > >> > >> And again, I think 6.0's improved dynamic-instantiation > >> queries are a > >> simple, already-built-in way to achieve that for most cases. > >> But I am open > >> to discussing a way to supply that combination via API if we > >> deem that > >> would be good - although then I'd also question how the current > >> TupleTransformer does not meet that need. > >> > >> On Thu, May 4, 2017 at 8:43 AM Steve Ebersole > >> <steve(a)hibernate.org <mailto:steve@hibernate.org>> wrote: > >> > >> > Were there a standard "represent something in XML-ish > >> format" contract > >> > portable across a number of formats (XML, JAXB, JSON, etc) > >> then I'd be more > >> > inclined to agree with this. But as it is, supporting this > >> would mean > >> > Hibernate implementing multiple such contracts, one per > >> format. However, > >> > > >> > 1. these formats are not our core competency > >> > 2. maintaining a complete set of these transformers > >> across all the > >> > popular formats du-jour is a large undertaking > >> > 3. I am not convinced that > >> > > >> > All of these increase the technical risk. > >> > > >> > Additionally, to properly support this we'd really need the > >> ability to > >> > then "map" multiple views for a given entity-graph-root. > >> What I mean by > >> > that, is that such DTO approaches often need multiple > >> "views" of a given > >> > entity, e.g. a CompanyListDTO, CompanyOverviewDTO, > >> > CompanyDetailsGeneralDTO, etc for a Company entity. The > >> point of this is > >> > that > >> > > >> > 1. the transformers for these are specific to each DTO > >> type and would > >> > be applied per-transformation > >> > 2. were Hibernate to "provide" this for applications > >> > > >> > IMO the use of queries to obtain views is logical. > >> Populating each of > >> > those specific DTOs (CompanyListDTO, etc) in the most > >> efficient way is > >> > going to require very different SQL for each DTO. This > >> implies some kind > >> > of "mapping" to be able associate each DTO with query. > >> > > >> > Given 6.0's improved dynamic-instantiation support, I even > >> think that is a > >> > great solution as well *for most cases*. > >> > > >> > So, while my objection has a "practical impact" component, > >> I also just > >> > question whether Hibernate integrating with each format's > >> "serializer" is > >> > the proper solution. > >> > > >> > > >> > > >> > On Thu, May 4, 2017 at 5:08 AM Christian Beikov < > >> > christian.beikov(a)gmail.com > >> <mailto:christian.beikov@gmail.com>> wrote: > >> > > >> >> This is exactly what I am trying to do with > >> Blaze-Persistence Entity > >> >> Views, making DTOs sexy and efficient :) > >> >> > >> >> Here a quick overview of how that looks like right now: > >> >> > >> >> > >> > https://persistence.blazebit.com/documentation/entity-view/ manual/en_US/index.html#first-entity-view-query > >> < > https://persistence.blazebit.com/documentation/entity-view/ manual/en_US/index.html#first-entity-view-query > > > >> >> > >> >> One of my targets is to make it possible to do something > >> like this > >> >> > >> >> entityManager.createQuery("FROM Order o", > >> OrderDTO.class).getResultList() > >> >> > >> >> and get an optimal query, as well as objects with only the > >> necessary > >> >> contents. > >> >> > >> >> Maybe we can collaborate on that somehow? > >> >> > >> >> > >> >> Mit freundlichen Grüßen, > >> >> > >> > ------------------------------------------------------------ ------------ > >> >> *Christian Beikov* > >> >> Am 04.05.2017 um 10:20 schrieb Emmanuel Bernard: > >> >> > Following up a bit on my previous email. > >> >> > > >> >> > While a core integration might be best I think, if there > >> are too much > >> >> > reluctance, we can start with a dedicated hibernate-dto > >> or whatever > >> >> > module or even separate project that makes life easier > >> for these "pass > >> >> > through" use cases. This could be in the form of a > >> wrapper API of sort > >> >> > and hence not affect existing Hibernate ORM APIs. > >> >> > > >> >> > Note that the ResultTransformer approach feels like it > >> goes a long way > >> >> > towards fixing the problem but as demonstrated in Vlad's > >> article > >> >> > > >> >> > >> > https://vladmihalcea.com/2017/04/03/why-you-should-use-the- hibernate-resulttransformer-to-customize-result-set-mappings/ > >> < > https://vladmihalcea.com/2017/04/03/why-you-should-use-the- hibernate-resulttransformer-to-customize-result-set-mappings/ > > > >> >> > it still requires quite a bit of code and a special DTO > >> constructor > >> >> > object. That's what we need to get rid of I think. > >> >> > > >> >> > Emmanuel > >> >> > > >> >> > On Thu 17-05-04 10:04, Emmanuel Bernard wrote: > >> >> >> I was very much in the Vlad, Steve, Christian camp > >> until relatively > >> >> >> recently. One of my main concern being that replacing a > >> proxy by null > >> >> >> was really sending the wrong message. So I was against > >> having Hibernate > >> >> >> ORM facilitate such a transformation. > >> >> >> > >> >> >> I am changing my mind because I am realizing that a lot > >> of applications > >> >> >> are less complex that my perceived median. A lot of > >> apps really just > >> >> >> want data to be fetched out and then passed to jackson > >> (implicitly) and > >> >> >> pushed out as a REST response in JSON or some other > >> serialization > >> >> >> protocol. > >> >> >> > >> >> >> So while we could try and keep the stance that such a > >> solution should > >> >> >> remain out of scope of Hibernate ORM core, we should > >> have a very smooth > >> >> >> integration with something like MapStruct to create > >> such bounded DTO on > >> >> >> the fly. Ideally with as close to zero code as possible > >> from the user > >> >> >> point of view. > >> >> >> I can't really describe how that could look like > >> because I am not > >> >> >> familiar enough with MapStruct but I think it should > >> have the following > >> >> >> characteristics: > >> >> >> > >> >> >> 1. do an implicit binding between the mapped object > >> graph and a > >> >> detached > >> >> >> object graph with a 1-1 mapping of type and > >> replacing lazy objects > >> >> and > >> >> >> collections with null. That's the smoothest approach > >> and the most > >> >> >> common use case but also the one where an > >> inexperienced person could > >> >> >> shoot at someone else's foot > >> >> >> 2. do a binding between the mapped object graph and a > >> detached version > >> >> of > >> >> >> that object graph with a 1-1 mapping of type, but > >> declaratively > >> >> >> expressing the boundaries for the detached version. > >> This enforces a > >> >> >> clear thinking of the boundaries and will load lazy > >> data in case the > >> >> >> object graph loaded is missing a bit. I like the > >> idea on principle > >> >> but > >> >> >> I think it overlaps a lot with the fetch graph. > >> >> >> 3. offer a full integration between MapStruct and > >> Hibernate ORM by > >> >> >> letting people express a full fledge MapStruct > >> transformation > >> >> between > >> >> >> the managed object graph and a different target > >> structure > >> >> >> > >> >> >> I favored MapStruct over Dozer because we know the > >> MapStruct lead > >> >> quite well ;) > >> >> >> > >> >> >> Note however that the MapStruct approach requires an > >> explicit object > >> >> >> copy, it feels a bit sad to have to double memory > >> consumption. But that > >> >> >> might be a good enough approach and bypassing the > >> managed object > >> >> >> creation leads to questions around the Persistence > >> Context contract > >> >> >> where loading an object supposedly means it will be in > >> the PC. > >> >> >> Maybe a constructor like query syntax allowing to > >> reference a MapStruct > >> >> >> conversion logic might work? > >> >> >> > >> >> >> select mapStruct('order-and-items', o) from Order o > >> left join > >> >> fetch o.items > >> >> >> > >> >> >> Emmanuel > >> >> >> > >> >> >> > >> >> >> On Wed 17-04-19 14:29, Vlad Mihalcea wrote: > >> >> >>> Hi, > >> >> >>> > >> >> >>> Although I keep on seeing this request from time to > >> time, I still > >> >> think > >> >> >>> it's more like a Code Smell. > >> >> >>> Entities are useful for when you plan to modify them. > >> Otherwise, a DTO > >> >> >>> projection is much more efficient, and you don't > >> suffer from > >> >> >>> LazyInitializationException. > >> >> >>> > >> >> >>> With the ResultTransformer, you can even build graphs > >> of entities, as > >> >> >>> explained in this article; > >> >> >>> > >> >> >>> > >> >> > >> > https://vladmihalcea.com/2017/04/03/why-you-should-use-the- hibernate-resulttransformer-to-customize-result-set-mappings/ > >> < > https://vladmihalcea.com/2017/04/03/why-you-should-use-the- hibernate-resulttransformer-to-customize-result-set-mappings/ > > > >> >> >>> > >> >> >>> Due to how Hibernate Proxies are handled, without > Bytecode > >> >> Enhancement, > >> >> >>> it's difficult to replace a Proxy with null after the > >> Session is > >> >> closed. If > >> >> >>> we implemented this, we'd have to take into > >> consideration both > >> >> Javassist > >> >> >>> and ByteBuddy as well as ByteCode Enhancements. > >> >> >>> > >> >> >>> all in all, the implementation effort might not > >> justify the benefit, > >> >> and > >> >> >>> I'm skeptical of offering a feature that does not > >> encourage data > >> >> access > >> >> >>> Best Practices. > >> >> >>> > >> >> >>> Vlad > >> >> >>> > >> >> >>> On Wed, Apr 19, 2017 at 2:18 PM, Christian Beikov < > >> >> >>> christian.beikov(a)gmail.com > >> <mailto:christian.beikov@gmail.com>> wrote: > >> >> >>> > >> >> >>>> Hey Romain, > >> >> >>>> > >> >> >>>> I don't think it is a good idea to expose entities > >> directly if you > >> >> >>>> really need a subset of the data. > >> >> >>>> Reasons for that thinking are that it gets hard to > >> define what needs > >> >> to > >> >> >>>> be fetched or is safe to be used for a particular use > >> case. Obviously > >> >> >>>> serialization is like a follow-up problem. > >> >> >>>> I see 2 possible solutions to the problem and both > >> boil down to the > >> >> use > >> >> >>>> of DTOs. > >> >> >>>> > >> >> >>>> 1. Use an object mapper(e.g. Dozer) that maps > >> entity object graphs > >> >> to > >> >> >>>> custom DTO types. > >> >> >>>> 2. Use specialized DTOs in queries. > >> >> >>>> > >> >> >>>> > >> >> >>>> Implementing 1. does not help you with lazy loading > >> issues and 2. > >> >> might > >> >> >>>> require very intrusive changes in queries which is > >> why I implemented > >> >> >>>> Blaze-Persistence Entity Views > >> >> >>>> > >> <https://github.com/beikov/blaze-persistence#entity-view- usage > >> <https://github.com/beikov/blaze-persistence#entity-view- usage > >>. > >> >> >>>> This is a library that allows you to define DTOs with > >> mappings to the > >> >> >>>> entity. In a query you can define that you want > >> results to be > >> >> >>>> "materialized" as instances of the DTO type. > >> >> >>>> This reduces the pain induced by properly separating the > >> >> "presentation > >> >> >>>> model" from the "persistence model" and at the same > >> time will improve > >> >> >>>> the performance by utilizing the mapping information. > >> >> >>>> I don't want to advertise too much, just wanted to > >> say that I had the > >> >> >>>> same issues over and over which is why I started that > >> project. > >> >> >>>> > >> >> >>>> Mit freundlichen Grüßen, > >> >> >>>> > >> >> > >> > ------------------------------------------------------------ ------------ > >> >> >>>> *Christian Beikov* > >> >> >>>> Am 19.04.2017 um 10:51 schrieb Romain Manni-Bucau: > >> >> >>>>> Hi guys, > >> >> >>>>> > >> >> >>>>> Short sumarry: Wonder if hibernate could get a > >> feature to kind of > >> >> either > >> >> >>>>> unproxy or freeze the entities once leaving the > >> managed context to > >> >> avoid > >> >> >>>>> uncontrolled lazy loading on one side and > >> serialization issues on > >> >> another > >> >> >>>>> side. > >> >> >>>>> > >> >> >>>>> Use case example: a common example is a REST service > >> exposing > >> >> directly > >> >> >>>>> hibernate entities (which is more and more common > >> with microservice > >> >> >>>>> "movement"). > >> >> >>>>> > >> >> >>>>> Objective: the goal is to not need any step - or > >> reduce them a lot - > >> >> >>>>> between the hibernate interaction and a potential > >> serialization to > >> >> avoid > >> >> >>>>> issues with lazy loading and unexpected loading. > >> Today it requires > >> >> some > >> >> >>>>> custom and hibernate specific logic in the > >> serializer which kind of > >> >> >>>> breaks > >> >> >>>>> the transversality of the two concerns > >> (serialization and object > >> >> >>>>> management/loading). > >> >> >>>>> > >> >> >>>>> > >> >> >>>>> Implementation options I see: > >> >> >>>>> > >> >> >>>>> 1. a callback requesting if the lazy relationship > >> should be fetched, > >> >> >>>>> something like > >> >> >>>>> > >> >> >>>>> public interface GraphVisitor { > >> >> >>>>> boolean shouldLoad(Object rootEntity, Property > >> property); > >> >> >>>>> } > >> >> >>>>> > >> >> >>>>> 2. An utility to remove any proxy potentially > >> throwing an exception > >> >> and > >> >> >>>>> replacing the value by null or an empty collection, > >> something like > >> >> >>>>> > >> >> >>>>> MyEntity e = Hibernate.deepUnproxy(entity); > >> >> >>>>> > >> >> >>>>> 3. A switch of the proxy implementation, this is > >> close to 2 but > >> >> wouldn't > >> >> >>>>> require a call to any utility, just a configuration > >> in the > >> >> persistence > >> >> >>>> unit. > >> >> >>>>> Side note: of course all 3 options can be mixed to > >> create a single > >> >> >>>> solution > >> >> >>>>> like having 3 implemented based on 1 for instance. > >> >> >>>>> > >> >> >>>>> Configuration proposal: this would be activated > >> through a property > >> >> in the > >> >> >>>>> persistence unit (this shouldn't be only global IMHO > >> cause > >> >> otherwise you > >> >> >>>>> can't mix 2 kind of units, like one for JSF and one > >> for JAX-RS to be > >> >> >>>>> concrete). This should also be activable as a query > >> hint i think - > >> >> but > >> >> >>>> more > >> >> >>>>> a nice to have. > >> >> >>>>> > >> >> >>>>> > >> >> >>>>> What this feature wouldn't be responsible for: > >> cycles. If > >> >> relationships > >> >> >>>> are > >> >> >>>>> bidirectional then the unproxied entity would still > >> "loop" if you > >> >> browse > >> >> >>>>> the object graph - this responsability would stay in > >> the consumer > >> >> since > >> >> >>>> it > >> >> >>>>> doesn't depend on hibernate directly but more on a > >> plain object > >> >> handling. > >> >> >>>>> > >> >> >>>>> What do you think? > >> >> >>>>> > >> >> >>>>> > >> >> >>>>> Romain Manni-Bucau > >> >> >>>>> @rmannibucau <https://twitter.com/rmannibucau > >> <https://twitter.com/rmannibucau>> | Blog > >> >> >>>>> <https://blog-rmannibucau.rhcloud.com > >> <https://blog-rmannibucau.rhcloud.com>> | Old Blog > >> >> >>>>> <http://rmannibucau.wordpress.com > >> <http://rmannibucau.wordpress.com>> | Github < > https://github.com/ > >> >> >>>> rmannibucau> | > >> >> >>>>> LinkedIn <https://www.linkedin.com/in/rmannibucau > >> <https://www.linkedin.com/in/rmannibucau>> | JavaEE Factory > >> >> >>>>> <https://javaeefactory-rmannibucau.rhcloud.com > >> <https://javaeefactory-rmannibucau.rhcloud.com>> > >> >> >>>>> _______________________________________________ > >> >> >>>>> hibernate-dev mailing list > >> >> >>>>> hibernate-dev(a)lists.jboss.org > >> <mailto:hibernate-dev@lists.jboss.org> > >> >> >>>>> > >> https://lists.jboss.org/mailman/listinfo/hibernate-dev > >> <https://lists.jboss.org/mailman/listinfo/hibernate-dev> > >> >> >>>> _______________________________________________ > >> >> >>>> hibernate-dev mailing list > >> >> >>>> hibernate-dev(a)lists.jboss.org > >> <mailto:hibernate-dev@lists.jboss.org> > >> >> >>>> > >> https://lists.jboss.org/mailman/listinfo/hibernate-dev > >> <https://lists.jboss.org/mailman/listinfo/hibernate-dev> > >> >> >>>> > >> >> >>> _______________________________________________ > >> >> >>> hibernate-dev mailing list > >> >> >>> hibernate-dev(a)lists.jboss.org > >> <mailto:hibernate-dev@lists.jboss.org> > >> >> >>> https://lists.jboss.org/mailman/listinfo/hibernate-dev > >> <https://lists.jboss.org/mailman/listinfo/hibernate-dev> > >> >> >> _______________________________________________ > >> >> >> hibernate-dev mailing list > >> >> >> hibernate-dev(a)lists.jboss.org > >> <mailto:hibernate-dev@lists.jboss.org> > >> >> >> https://lists.jboss.org/mailman/listinfo/hibernate-dev > >> <https://lists.jboss.org/mailman/listinfo/hibernate-dev> > >> >> > _______________________________________________ > >> >> > hibernate-dev mailing list > >> >> > hibernate-dev(a)lists.jboss.org > >> <mailto:hibernate-dev@lists.jboss.org> > >> >> > https://lists.jboss.org/mailman/listinfo/hibernate-dev > >> <https://lists.jboss.org/mailman/listinfo/hibernate-dev> > >> >> > >> >> _______________________________________________ > >> >> hibernate-dev mailing list > >> >> hibernate-dev(a)lists.jboss.org > >> <mailto:hibernate-dev@lists.jboss.org> > >> >> https://lists.jboss.org/mailman/listinfo/hibernate-dev > >> <https://lists.jboss.org/mailman/listinfo/hibernate-dev> > >> >> > >> > > >> _______________________________________________ > >> hibernate-dev mailing list > >> hibernate-dev(a)lists.jboss.org > >> <mailto:hibernate-dev@lists.jboss.org> > >> https://lists.jboss.org/mailman/listinfo/hibernate-dev > >> <https://lists.jboss.org/mailman/listinfo/hibernate-dev> > >> > > > > > > _______________________________________________ > hibernate-dev mailing list > hibernate-dev(a)lists.jboss.org > https://lists.jboss.org/mailman/listinfo/hibernate-dev _______________________________________________ hibernate-dev mailing list hibernate-dev(a)lists.jboss.org https://lists.jboss.org/mailman/listinfo/hibernate-dev

Detecting if an object is initialized should be as easy as calling " Hibernate.isInitialized(object)". If you want to know whether a specic attribute of an object is initialized you'd use "Hibernate.isPropertyInitialized(object, attributeName)". What you want is some kind of integration that makes use of these two methods, so that if they return false, a null value is used when serializing objects to XML/JSON via JAXB/JSONB. Is that correct?

I don't know of any hook in JAXB that could be used to put that code into so it works out as you'd expect it. The only other way I can think of, is nulling the properties explicitly which could be done quite easily. You probably gonna need just a single recursive method to do that. I don't see how that method should be part of Hibernate nor how you'd expect to be able to configure Hibernate so that it would do that transparently.

I still think the cleanest solution would be to have DTOs, which is why I'd argue that such a halve solution shouldn't be part of Hibernate.

Mit freundlichen Grüßen, ------------------------------ *Christian Beikov* Am 04.05.2017 um 18:00 schrieb Romain Manni-Bucau: 2017-05-04 17:33 GMT+02:00 Steve Ebersole <steve(a)hibernate.org&gt;: > What exactly would this "utility one level further than existing ones" do? > > Multiple options are possible but one is to return null instead of throwing lazy exception for instance. > And for what it is worth, IMO the new Navigable model in 6.0 will again > help here. Especially in conjunction with the Navigable visitation > support. > I'm not familiar enough but if it providers for each member a way to know if it is loaded or not it can work. > > On Thu, May 4, 2017 at 10:27 AM Christian Beikov < > christian.beikov(a)gmail.com&gt; > wrote: > > > Well that is again exactly what a DTO is good for. If you as developer > > want the groups to be available, you add a list of groups to that > > special DTO type for that use case. In your data access layer you > > somehow populate that, which is normally done by using some mapper > > library like MapStruct or Dozer and then JAXB/JSONB can just work with > > the DTO type without any problems. > > > > Now if you forget to add a JOIN FETCH to your query and you end up with > > N+1 queries, that's a different problem, just like the amount of > > boilerplate code needed for having DTO types for every use case. That I > > try to solve with Blaze-Persistence Entity Views. > > > > Just a quick example to make my point here. If you have a REST endpoint > > /user/{id} and want to provide the list of group names along with the > > user information, you'd create a UserInfoDTO. > > > > @EntityView(User.class) > > interface UserInfoDTO { > > String getUsername(); > > @Mapping("groups.name") > > List<String> getGroups(); > > } > > > > Your repository returns an object of that type and you just pass that > > object through so JAXB/JSONB can do their work. The mapping information > > in the DTO is applied on a "source query" i.e. only doing the work > > absolutely necessary to satisfy the requested projection. > > > > Implementing this by hand is by no means impossible, but rather > > inconvenient I'd say, which is probably why you are seeking for other > > solutions. > > > > In the end, you can only try to create a minimal DTO that has exactly > > the fields you want to be serialized or annotate your existing entities > > with those "ignore" annotations and hope for the best. I don't see how > > hibernate could or should help in any of the two cases. > > > > Mit freundlichen Grüßen, > > ------------------------------------------------------------ > ------------ > > *Christian Beikov* > > Am 04.05.2017 um 16:59 schrieb Romain Manni-Bucau: > > > Sure. If you add any conversion logic then you are clearly out of > > > hibernate scope and the problem doesnt appear anymore. Here is a > > > trivial example (hopefully trivial at least ;)) > > > > > > User 1 - n Group > > > > > > In json we would get something like {username:...,groups:[group1, > > > group2]}, no issue to know if group should be loaded or not since this > > > part of the logic is in the mapper layer. > > > > > > So yes you can say "not my problem" but next framework will > > > immediately ask "how do i know" and you likely end like all > > > spring-data-rest recommandation with a specific mapping and not a > > > framework solution which is the target of that thread - at least what > > > I tried to explain ;). > > > > > > 2017-05-04 16:41 GMT+02:00 Christian Beikov > > > <christian.beikov(a)gmail.com <mailto:christian.beikov@gmail.com>>: > > > > > > I don't understand what you mean by "you put that logic in the > > > conversion", could you elaborate? > > > > > > > > > Mit freundlichen Grüßen, > > > > > ------------------------------------------------------------ > ------------ > > > *Christian Beikov* > > > Am 04.05.2017 um 16:32 schrieb Romain Manni-Bucau: > > >> Few more points: > > >> > > >> 1. Dto dont help at any moment - or you put that logic in the > > >> conversion and you are back to start > > >> 2. Making jaxb/jsonb easy to integrate is the goal IMO. No need > > >> to integrate with them but just provide some utility one level > > >> further than existing ones > > >> > > >> Le 4 mai 2017 16:13, "Steve Ebersole" <steve(a)hibernate.org > > >> <mailto:steve@hibernate.org>> a écrit : > > >> > > >> Oops, that (3) in previous reply should have read: > > >> 3. supporting each format creates a new "optional" library > > >> dependency > > >> > > >> Overall, I like Christian's approach as a potential > > >> generalized approach to > > >> this. Basically a combination of > > >> > > >> 1. a query used to provide the "view source values" > > >> 2. some indication of how to map those "source values" to > > >> your view model > > >> > > >> > > >> And again, I think 6.0's improved dynamic-instantiation > > >> queries are a > > >> simple, already-built-in way to achieve that for most cases. > > >> But I am open > > >> to discussing a way to supply that combination via API if we > > >> deem that > > >> would be good - although then I'd also question how the > current > > >> TupleTransformer does not meet that need. > > >> > > >> On Thu, May 4, 2017 at 8:43 AM Steve Ebersole > > >> <steve(a)hibernate.org <mailto:steve@hibernate.org>> wrote: > > >> > > >> > Were there a standard "represent something in XML-ish > > >> format" contract > > >> > portable across a number of formats (XML, JAXB, JSON, etc) > > >> then I'd be more > > >> > inclined to agree with this. But as it is, supporting this > > >> would mean > > >> > Hibernate implementing multiple such contracts, one per > > >> format. However, > > >> > > > >> > 1. these formats are not our core competency > > >> > 2. maintaining a complete set of these transformers > > >> across all the > > >> > popular formats du-jour is a large undertaking > > >> > 3. I am not convinced that > > >> > > > >> > All of these increase the technical risk. > > >> > > > >> > Additionally, to properly support this we'd really need the > > >> ability to > > >> > then "map" multiple views for a given entity-graph-root. > > >> What I mean by > > >> > that, is that such DTO approaches often need multiple > > >> "views" of a given > > >> > entity, e.g. a CompanyListDTO, CompanyOverviewDTO, > > >> > CompanyDetailsGeneralDTO, etc for a Company entity. The > > >> point of this is > > >> > that > > >> > > > >> > 1. the transformers for these are specific to each DTO > > >> type and would > > >> > be applied per-transformation > > >> > 2. were Hibernate to "provide" this for applications > > >> > > > >> > IMO the use of queries to obtain views is logical. > > >> Populating each of > > >> > those specific DTOs (CompanyListDTO, etc) in the most > > >> efficient way is > > >> > going to require very different SQL for each DTO. This > > >> implies some kind > > >> > of "mapping" to be able associate each DTO with query. > > >> > > > >> > Given 6.0's improved dynamic-instantiation support, I even > > >> think that is a > > >> > great solution as well *for most cases*. > > >> > > > >> > So, while my objection has a "practical impact" component, > > >> I also just > > >> > question whether Hibernate integrating with each format's > > >> "serializer" is > > >> > the proper solution. > > >> > > > >> > > > >> > > > >> > On Thu, May 4, 2017 at 5:08 AM Christian Beikov < > > >> > christian.beikov(a)gmail.com > > >> <mailto:christian.beikov@gmail.com>> wrote: > > >> > > > >> >> This is exactly what I am trying to do with > > >> Blaze-Persistence Entity > > >> >> Views, making DTOs sexy and efficient :) > > >> >> > > >> >> Here a quick overview of how that looks like right now: > > >> >> > > >> >> > > >> > > https://persistence.blazebit.com/documentation/entity-view/m > anual/en_US/index.html#first-entity-view-query > > >> < > > https://persistence.blazebit.com/documentation/entity-view/m > anual/en_US/index.html#first-entity-view-query > > > > > >> >> > > >> >> One of my targets is to make it possible to do something > > >> like this > > >> >> > > >> >> entityManager.createQuery("FROM Order o", > > >> OrderDTO.class).getResultList() > > >> >> > > >> >> and get an optimal query, as well as objects with only the > > >> necessary > > >> >> contents. > > >> >> > > >> >> Maybe we can collaborate on that somehow? > > >> >> > > >> >> > > >> >> Mit freundlichen Grüßen, > > >> >> > > >> > > ------------------------------------------------------------ > ------------ > > >> >> *Christian Beikov* > > >> >> Am 04.05.2017 um 10:20 schrieb Emmanuel Bernard: > > >> >> > Following up a bit on my previous email. > > >> >> > > > >> >> > While a core integration might be best I think, if there > > >> are too much > > >> >> > reluctance, we can start with a dedicated hibernate-dto > > >> or whatever > > >> >> > module or even separate project that makes life easier > > >> for these "pass > > >> >> > through" use cases. This could be in the form of a > > >> wrapper API of sort > > >> >> > and hence not affect existing Hibernate ORM APIs. > > >> >> > > > >> >> > Note that the ResultTransformer approach feels like it > > >> goes a long way > > >> >> > towards fixing the problem but as demonstrated in Vlad's > > >> article > > >> >> > > > >> >> > > >> > > https://vladmihalcea.com/2017/04/03/why-you-should-use-the-h > ibernate-resulttransformer-to-customize-result-set-mappings/ > > >> < > > https://vladmihalcea.com/2017/04/03/why-you-should-use-the-h > ibernate-resulttransformer-to-customize-result-set-mappings/ > > > > > >> >> > it still requires quite a bit of code and a special DTO > > >> constructor > > >> >> > object. That's what we need to get rid of I think. > > >> >> > > > >> >> > Emmanuel > > >> >> > > > >> >> > On Thu 17-05-04 10:04, Emmanuel Bernard wrote: > > >> >> >> I was very much in the Vlad, Steve, Christian camp > > >> until relatively > > >> >> >> recently. One of my main concern being that replacing a > > >> proxy by null > > >> >> >> was really sending the wrong message. So I was against > > >> having Hibernate > > >> >> >> ORM facilitate such a transformation. > > >> >> >> > > >> >> >> I am changing my mind because I am realizing that a lot > > >> of applications > > >> >> >> are less complex that my perceived median. A lot of > > >> apps really just > > >> >> >> want data to be fetched out and then passed to jackson > > >> (implicitly) and > > >> >> >> pushed out as a REST response in JSON or some other > > >> serialization > > >> >> >> protocol. > > >> >> >> > > >> >> >> So while we could try and keep the stance that such a > > >> solution should > > >> >> >> remain out of scope of Hibernate ORM core, we should > > >> have a very smooth > > >> >> >> integration with something like MapStruct to create > > >> such bounded DTO on > > >> >> >> the fly. Ideally with as close to zero code as possible > > >> from the user > > >> >> >> point of view. > > >> >> >> I can't really describe how that could look like > > >> because I am not > > >> >> >> familiar enough with MapStruct but I think it should > > >> have the following > > >> >> >> characteristics: > > >> >> >> > > >> >> >> 1. do an implicit binding between the mapped object > > >> graph and a > > >> >> detached > > >> >> >> object graph with a 1-1 mapping of type and > > >> replacing lazy objects > > >> >> and > > >> >> >> collections with null. That's the smoothest approach > > >> and the most > > >> >> >> common use case but also the one where an > > >> inexperienced person could > > >> >> >> shoot at someone else's foot > > >> >> >> 2. do a binding between the mapped object graph and a > > >> detached version > > >> >> of > > >> >> >> that object graph with a 1-1 mapping of type, but > > >> declaratively > > >> >> >> expressing the boundaries for the detached version. > > >> This enforces a > > >> >> >> clear thinking of the boundaries and will load lazy > > >> data in case the > > >> >> >> object graph loaded is missing a bit. I like the > > >> idea on principle > > >> >> but > > >> >> >> I think it overlaps a lot with the fetch graph. > > >> >> >> 3. offer a full integration between MapStruct and > > >> Hibernate ORM by > > >> >> >> letting people express a full fledge MapStruct > > >> transformation > > >> >> between > > >> >> >> the managed object graph and a different target > > >> structure > > >> >> >> > > >> >> >> I favored MapStruct over Dozer because we know the > > >> MapStruct lead > > >> >> quite well ;) > > >> >> >> > > >> >> >> Note however that the MapStruct approach requires an > > >> explicit object > > >> >> >> copy, it feels a bit sad to have to double memory > > >> consumption. But that > > >> >> >> might be a good enough approach and bypassing the > > >> managed object > > >> >> >> creation leads to questions around the Persistence > > >> Context contract > > >> >> >> where loading an object supposedly means it will be in > > >> the PC. > > >> >> >> Maybe a constructor like query syntax allowing to > > >> reference a MapStruct > > >> >> >> conversion logic might work? > > >> >> >> > > >> >> >> select mapStruct('order-and-items', o) from Order o > > >> left join > > >> >> fetch o.items > > >> >> >> > > >> >> >> Emmanuel > > >> >> >> > > >> >> >> > > >> >> >> On Wed 17-04-19 14:29, Vlad Mihalcea wrote: > > >> >> >>> Hi, > > >> >> >>> > > >> >> >>> Although I keep on seeing this request from time to > > >> time, I still > > >> >> think > > >> >> >>> it's more like a Code Smell. > > >> >> >>> Entities are useful for when you plan to modify them. > > >> Otherwise, a DTO > > >> >> >>> projection is much more efficient, and you don't > > >> suffer from > > >> >> >>> LazyInitializationException. > > >> >> >>> > > >> >> >>> With the ResultTransformer, you can even build graphs > > >> of entities, as > > >> >> >>> explained in this article; > > >> >> >>> > > >> >> >>> > > >> >> > > >> > > https://vladmihalcea.com/2017/04/03/why-you-should-use-the-h > ibernate-resulttransformer-to-customize-result-set-mappings/ > > >> < > > https://vladmihalcea.com/2017/04/03/why-you-should-use-the-h > ibernate-resulttransformer-to-customize-result-set-mappings/ > > > > > >> >> >>> > > >> >> >>> Due to how Hibernate Proxies are handled, without > > Bytecode > > >> >> Enhancement, > > >> >> >>> it's difficult to replace a Proxy with null after the > > >> Session is > > >> >> closed. If > > >> >> >>> we implemented this, we'd have to take into > > >> consideration both > > >> >> Javassist > > >> >> >>> and ByteBuddy as well as ByteCode Enhancements. > > >> >> >>> > > >> >> >>> all in all, the implementation effort might not > > >> justify the benefit, > > >> >> and > > >> >> >>> I'm skeptical of offering a feature that does not > > >> encourage data > > >> >> access > > >> >> >>> Best Practices. > > >> >> >>> > > >> >> >>> Vlad > > >> >> >>> > > >> >> >>> On Wed, Apr 19, 2017 at 2:18 PM, Christian Beikov < > > >> >> >>> christian.beikov(a)gmail.com > > >> <mailto:christian.beikov@gmail.com>> wrote: > > >> >> >>> > > >> >> >>>> Hey Romain, > > >> >> >>>> > > >> >> >>>> I don't think it is a good idea to expose entities > > >> directly if you > > >> >> >>>> really need a subset of the data. > > >> >> >>>> Reasons for that thinking are that it gets hard to > > >> define what needs > > >> >> to > > >> >> >>>> be fetched or is safe to be used for a particular use > > >> case. Obviously > > >> >> >>>> serialization is like a follow-up problem. > > >> >> >>>> I see 2 possible solutions to the problem and both > > >> boil down to the > > >> >> use > > >> >> >>>> of DTOs. > > >> >> >>>> > > >> >> >>>> 1. Use an object mapper(e.g. Dozer) that maps > > >> entity object graphs > > >> >> to > > >> >> >>>> custom DTO types. > > >> >> >>>> 2. Use specialized DTOs in queries. > > >> >> >>>> > > >> >> >>>> > > >> >> >>>> Implementing 1. does not help you with lazy loading > > >> issues and 2. > > >> >> might > > >> >> >>>> require very intrusive changes in queries which is > > >> why I implemented > > >> >> >>>> Blaze-Persistence Entity Views > > >> >> >>>> > > >> <https://github.com/beikov/blaze-persistence#entity-view-us > age > > >> <https://github.com/beikov/blaze-persistence#entity-view-us > age > > >>. > > >> >> >>>> This is a library that allows you to define DTOs with > > >> mappings to the > > >> >> >>>> entity. In a query you can define that you want > > >> results to be > > >> >> >>>> "materialized" as instances of the DTO type. > > >> >> >>>> This reduces the pain induced by properly separating > the > > >> >> "presentation > > >> >> >>>> model" from the "persistence model" and at the same > > >> time will improve > > >> >> >>>> the performance by utilizing the mapping information. > > >> >> >>>> I don't want to advertise too much, just wanted to > > >> say that I had the > > >> >> >>>> same issues over and over which is why I started that > > >> project. > > >> >> >>>> > > >> >> >>>> Mit freundlichen Grüßen, > > >> >> >>>> > > >> >> > > >> > > ------------------------------------------------------------ > ------------ > > >> >> >>>> *Christian Beikov* > > >> >> >>>> Am 19.04.2017 um 10:51 schrieb Romain Manni-Bucau: > > >> >> >>>>> Hi guys, > > >> >> >>>>> > > >> >> >>>>> Short sumarry: Wonder if hibernate could get a > > >> feature to kind of > > >> >> either > > >> >> >>>>> unproxy or freeze the entities once leaving the > > >> managed context to > > >> >> avoid > > >> >> >>>>> uncontrolled lazy loading on one side and > > >> serialization issues on > > >> >> another > > >> >> >>>>> side. > > >> >> >>>>> > > >> >> >>>>> Use case example: a common example is a REST service > > >> exposing > > >> >> directly > > >> >> >>>>> hibernate entities (which is more and more common > > >> with microservice > > >> >> >>>>> "movement"). > > >> >> >>>>> > > >> >> >>>>> Objective: the goal is to not need any step - or > > >> reduce them a lot - > > >> >> >>>>> between the hibernate interaction and a potential > > >> serialization to > > >> >> avoid > > >> >> >>>>> issues with lazy loading and unexpected loading. > > >> Today it requires > > >> >> some > > >> >> >>>>> custom and hibernate specific logic in the > > >> serializer which kind of > > >> >> >>>> breaks > > >> >> >>>>> the transversality of the two concerns > > >> (serialization and object > > >> >> >>>>> management/loading). > > >> >> >>>>> > > >> >> >>>>> > > >> >> >>>>> Implementation options I see: > > >> >> >>>>> > > >> >> >>>>> 1. a callback requesting if the lazy relationship > > >> should be fetched, > > >> >> >>>>> something like > > >> >> >>>>> > > >> >> >>>>> public interface GraphVisitor { > > >> >> >>>>> boolean shouldLoad(Object rootEntity, Property > > >> property); > > >> >> >>>>> } > > >> >> >>>>> > > >> >> >>>>> 2. An utility to remove any proxy potentially > > >> throwing an exception > > >> >> and > > >> >> >>>>> replacing the value by null or an empty collection, > > >> something like > > >> >> >>>>> > > >> >> >>>>> MyEntity e = Hibernate.deepUnproxy(entity); > > >> >> >>>>> > > >> >> >>>>> 3. A switch of the proxy implementation, this is > > >> close to 2 but > > >> >> wouldn't > > >> >> >>>>> require a call to any utility, just a configuration > > >> in the > > >> >> persistence > > >> >> >>>> unit. > > >> >> >>>>> Side note: of course all 3 options can be mixed to > > >> create a single > > >> >> >>>> solution > > >> >> >>>>> like having 3 implemented based on 1 for instance. > > >> >> >>>>> > > >> >> >>>>> Configuration proposal: this would be activated > > >> through a property > > >> >> in the > > >> >> >>>>> persistence unit (this shouldn't be only global IMHO > > >> cause > > >> >> otherwise you > > >> >> >>>>> can't mix 2 kind of units, like one for JSF and one > > >> for JAX-RS to be > > >> >> >>>>> concrete). This should also be activable as a query > > >> hint i think - > > >> >> but > > >> >> >>>> more > > >> >> >>>>> a nice to have. > > >> >> >>>>> > > >> >> >>>>> > > >> >> >>>>> What this feature wouldn't be responsible for: > > >> cycles. If > > >> >> relationships > > >> >> >>>> are > > >> >> >>>>> bidirectional then the unproxied entity would still > > >> "loop" if you > > >> >> browse > > >> >> >>>>> the object graph - this responsability would stay in > > >> the consumer > > >> >> since > > >> >> >>>> it > > >> >> >>>>> doesn't depend on hibernate directly but more on a > > >> plain object > > >> >> handling. > > >> >> >>>>> > > >> >> >>>>> What do you think? > > >> >> >>>>> > > >> >> >>>>> > > >> >> >>>>> Romain Manni-Bucau > > >> >> >>>>> @rmannibucau <https://twitter.com/rmannibucau > > >> <https://twitter.com/rmannibucau>> | Blog > > >> >> >>>>> <https://blog-rmannibucau.rhcloud.com > > >> <https://blog-rmannibucau.rhcloud.com>> | Old Blog > > >> >> >>>>> <http://rmannibucau.wordpress.com > > >> <http://rmannibucau.wordpress.com>> | Github < > > https://github.com/ > > >> >> >>>> rmannibucau> | > > >> >> >>>>> LinkedIn <https://www.linkedin.com/in/rmannibucau > > >> <https://www.linkedin.com/in/rmannibucau>> | JavaEE Factory > > >> >> >>>>> <https://javaeefactory-rmannibucau.rhcloud.com > > >> <https://javaeefactory-rmannibucau.rhcloud.com>> > > >> >> >>>>> _______________________________________________ > > >> >> >>>>> hibernate-dev mailing list > > >> >> >>>>> hibernate-dev(a)lists.jboss.org > > >> <mailto:hibernate-dev@lists.jboss.org> > > >> >> >>>>> > > >> https://lists.jboss.org/mailman/listinfo/hibernate-dev > > >> <https://lists.jboss.org/mailman/listinfo/hibernate-dev> > > >> >> >>>> _______________________________________________ > > >> >> >>>> hibernate-dev mailing list > > >> >> >>>> hibernate-dev(a)lists.jboss.org > > >> <mailto:hibernate-dev@lists.jboss.org> > > >> >> >>>> > > >> https://lists.jboss.org/mailman/listinfo/hibernate-dev > > >> <https://lists.jboss.org/mailman/listinfo/hibernate-dev> > > >> >> >>>> > > >> >> >>> _______________________________________________ > > >> >> >>> hibernate-dev mailing list > > >> >> >>> hibernate-dev(a)lists.jboss.org > > >> <mailto:hibernate-dev@lists.jboss.org> > > >> >> >>> https://lists.jboss.org/mailma > n/listinfo/hibernate-dev > > >> <https://lists.jboss.org/mailman/listinfo/hibernate-dev> > > >> >> >> _______________________________________________ > > >> >> >> hibernate-dev mailing list > > >> >> >> hibernate-dev(a)lists.jboss.org > > >> <mailto:hibernate-dev@lists.jboss.org> > > >> >> >> https://lists.jboss.org/mailman/listinfo/hibernate-dev > > >> <https://lists.jboss.org/mailman/listinfo/hibernate-dev> > > >> >> > _______________________________________________ > > >> >> > hibernate-dev mailing list > > >> >> > hibernate-dev(a)lists.jboss.org > > >> <mailto:hibernate-dev@lists.jboss.org> > > >> >> > https://lists.jboss.org/mailman/listinfo/hibernate-dev > > >> <https://lists.jboss.org/mailman/listinfo/hibernate-dev> > > >> >> > > >> >> _______________________________________________ > > >> >> hibernate-dev mailing list > > >> >> hibernate-dev(a)lists.jboss.org > > >> <mailto:hibernate-dev@lists.jboss.org> > > >> >> https://lists.jboss.org/mailman/listinfo/hibernate-dev > > >> <https://lists.jboss.org/mailman/listinfo/hibernate-dev> > > >> >> > > >> > > > >> _______________________________________________ > > >> hibernate-dev mailing list > > >> hibernate-dev(a)lists.jboss.org > > >> <mailto:hibernate-dev@lists.jboss.org> > > >> https://lists.jboss.org/mailman/listinfo/hibernate-dev > > >> <https://lists.jboss.org/mailman/listinfo/hibernate-dev> > > >> > > > > > > > > > > _______________________________________________ > > hibernate-dev mailing list > > hibernate-dev(a)lists.jboss.org > > https://lists.jboss.org/mailman/listinfo/hibernate-dev > _______________________________________________ > hibernate-dev mailing list > hibernate-dev(a)lists.jboss.org > https://lists.jboss.org/mailman/listinfo/hibernate-dev >

But your psuedo code is really just the same as: AnEntity e = find(); if ( isInitialized( e ) ) { serializer.serialize(e); }

boolean isInitialized(Object e) { return Hibernate.isInitialized( e ); } What I was getting at with the 6.0 + Navigavble discussion is that it would be better to base this "isInitialized" on these Navigables instead. A Navigable is a polymorphic reference that might be an entity, a persistent attribute, a "collection element", etc.

On Thu, May 4, 2017 at 11:46 AM Romain Manni-Bucau <rmannibucau(a)gmail.com&gt; wrote: > 2017-05-04 18:42 GMT+02:00 Christian Beikov <christian.beikov(a)gmail.com&gt;: > >> Detecting if an object is initialized should be as easy as calling " >> Hibernate.isInitialized(object)". If you want to know whether a specic >> attribute of an object is initialized you'd use "Hibernate.isPropertyInitialized(object, >> attributeName)". What you want is some kind of integration that makes >> use of these two methods, so that if they return false, a null value is >> used when serializing objects to XML/JSON via JAXB/JSONB. Is that correct? >> > > Almost, I would like one able to just disable it, this way the serializer > doesnt need anything or knowledge of hibernate. Worse case we need to > integrate with the serializer in a way close to the one i proposed for > johnzon before. > > In pseudo code it would be: > > AnEntity e = find(); > Hibernate.disableLazyExceptionWithNull(e); > serializer.serialize(e); > > >> I don't know of any hook in JAXB that could be used to put that code >> into so it works out as you'd expect it. The only other way I can think of, >> is nulling the properties explicitly which could be done quite easily. You >> probably gonna need just a single recursive method to do that. I don't see >> how that method should be part of Hibernate nor how you'd expect to be able >> to configure Hibernate so that it would do that transparently. >> > the switch of lazyexception to null would work wit jaxb. Otherwise you > need some more low level integration not portable IIRC. > > >> I still think the cleanest solution would be to have DTOs, which is why >> I'd argue that such a halve solution shouldn't be part of Hibernate. >> > > Think we all agree (or agreed already ;)) but created this thread cause i > saw it often enough to be a need. > > >> >> Mit freundlichen Grüßen, >> ------------------------------ >> *Christian Beikov* >> Am 04.05.2017 um 18:00 schrieb Romain Manni-Bucau: >> >> >> >> 2017-05-04 17:33 GMT+02:00 Steve Ebersole <steve(a)hibernate.org&gt;: >> >>> What exactly would this "utility one level further than existing ones" >>> do? >>> >>> >> Multiple options are possible but one is to return null instead of >> throwing lazy exception for instance. >> >> >>> And for what it is worth, IMO the new Navigable model in 6.0 will again >>> help here. Especially in conjunction with the Navigable visitation >>> support. >>> >> >> I'm not familiar enough but if it providers for each member a way to >> know if it is loaded or not it can work. >> >> >>> >>> On Thu, May 4, 2017 at 10:27 AM Christian Beikov < >>> christian.beikov(a)gmail.com&gt; >>> wrote: >>> >>> > Well that is again exactly what a DTO is good for. If you as developer >>> > want the groups to be available, you add a list of groups to that >>> > special DTO type for that use case. In your data access layer you >>> > somehow populate that, which is normally done by using some mapper >>> > library like MapStruct or Dozer and then JAXB/JSONB can just work with >>> > the DTO type without any problems. >>> > >>> > Now if you forget to add a JOIN FETCH to your query and you end up >>> with >>> > N+1 queries, that's a different problem, just like the amount of >>> > boilerplate code needed for having DTO types for every use case. That >>> I >>> > try to solve with Blaze-Persistence Entity Views. >>> > >>> > Just a quick example to make my point here. If you have a REST >>> endpoint >>> > /user/{id} and want to provide the list of group names along with the >>> > user information, you'd create a UserInfoDTO. >>> > >>> > @EntityView(User.class) >>> > interface UserInfoDTO { >>> > String getUsername(); >>> > @Mapping("groups.name") >>> > List<String> getGroups(); >>> > } >>> > >>> > Your repository returns an object of that type and you just pass that >>> > object through so JAXB/JSONB can do their work. The mapping >>> information >>> > in the DTO is applied on a "source query" i.e. only doing the work >>> > absolutely necessary to satisfy the requested projection. >>> > >>> > Implementing this by hand is by no means impossible, but rather >>> > inconvenient I'd say, which is probably why you are seeking for other >>> > solutions. >>> > >>> > In the end, you can only try to create a minimal DTO that has exactly >>> > the fields you want to be serialized or annotate your existing >>> entities >>> > with those "ignore" annotations and hope for the best. I don't see how >>> > hibernate could or should help in any of the two cases. >>> > >>> > Mit freundlichen Grüßen, >>> > ------------------------------------------------------------ >>> ------------ >>> > *Christian Beikov* >>> > Am 04.05.2017 um 16:59 schrieb Romain Manni-Bucau: >>> > > Sure. If you add any conversion logic then you are clearly out of >>> > > hibernate scope and the problem doesnt appear anymore. Here is a >>> > > trivial example (hopefully trivial at least ;)) >>> > > >>> > > User 1 - n Group >>> > > >>> > > In json we would get something like {username:...,groups:[group1, >>> > > group2]}, no issue to know if group should be loaded or not since >>> this >>> > > part of the logic is in the mapper layer. >>> > > >>> > > So yes you can say "not my problem" but next framework will >>> > > immediately ask "how do i know" and you likely end like all >>> > > spring-data-rest recommandation with a specific mapping and not a >>> > > framework solution which is the target of that thread - at least >>> what >>> > > I tried to explain ;). >>> > > >>> > > 2017-05-04 16:41 GMT+02:00 Christian Beikov >>> > > <christian.beikov(a)gmail.com <mailto:christian.beikov@gmail.com>>: >>> > > >>> > > I don't understand what you mean by "you put that logic in the >>> > > conversion", could you elaborate? >>> > > >>> > > >>> > > Mit freundlichen Grüßen, >>> > > >>> > ------------------------------------------------------------ >>> ------------ >>> > > *Christian Beikov* >>> > > Am 04.05.2017 um 16:32 schrieb Romain Manni-Bucau: >>> > >> Few more points: >>> > >> >>> > >> 1. Dto dont help at any moment - or you put that logic in the >>> > >> conversion and you are back to start >>> > >> 2. Making jaxb/jsonb easy to integrate is the goal IMO. No need >>> > >> to integrate with them but just provide some utility one level >>> > >> further than existing ones >>> > >> >>> > >> Le 4 mai 2017 16:13, "Steve Ebersole" <steve(a)hibernate.org >>> > >> <mailto:steve@hibernate.org>> a écrit : >>> > >> >>> > >> Oops, that (3) in previous reply should have read: >>> > >> 3. supporting each format creates a new "optional" library >>> > >> dependency >>> > >> >>> > >> Overall, I like Christian's approach as a potential >>> > >> generalized approach to >>> > >> this. Basically a combination of >>> > >> >>> > >> 1. a query used to provide the "view source values" >>> > >> 2. some indication of how to map those "source values" >>> to >>> > >> your view model >>> > >> >>> > >> >>> > >> And again, I think 6.0's improved dynamic-instantiation >>> > >> queries are a >>> > >> simple, already-built-in way to achieve that for most >>> cases. >>> > >> But I am open >>> > >> to discussing a way to supply that combination via API if >>> we >>> > >> deem that >>> > >> would be good - although then I'd also question how the >>> current >>> > >> TupleTransformer does not meet that need. >>> > >> >>> > >> On Thu, May 4, 2017 at 8:43 AM Steve Ebersole >>> > >> <steve(a)hibernate.org <mailto:steve@hibernate.org>> wrote: >>> > >> >>> > >> > Were there a standard "represent something in XML-ish >>> > >> format" contract >>> > >> > portable across a number of formats (XML, JAXB, JSON, >>> etc) >>> > >> then I'd be more >>> > >> > inclined to agree with this. But as it is, supporting >>> this >>> > >> would mean >>> > >> > Hibernate implementing multiple such contracts, one per >>> > >> format. However, >>> > >> > >>> > >> > 1. these formats are not our core competency >>> > >> > 2. maintaining a complete set of these transformers >>> > >> across all the >>> > >> > popular formats du-jour is a large undertaking >>> > >> > 3. I am not convinced that >>> > >> > >>> > >> > All of these increase the technical risk. >>> > >> > >>> > >> > Additionally, to properly support this we'd really need >>> the >>> > >> ability to >>> > >> > then "map" multiple views for a given entity-graph-root. >>> > >> What I mean by >>> > >> > that, is that such DTO approaches often need multiple >>> > >> "views" of a given >>> > >> > entity, e.g. a CompanyListDTO, CompanyOverviewDTO, >>> > >> > CompanyDetailsGeneralDTO, etc for a Company entity. The >>> > >> point of this is >>> > >> > that >>> > >> > >>> > >> > 1. the transformers for these are specific to each DTO >>> > >> type and would >>> > >> > be applied per-transformation >>> > >> > 2. were Hibernate to "provide" this for applications >>> > >> > >>> > >> > IMO the use of queries to obtain views is logical. >>> > >> Populating each of >>> > >> > those specific DTOs (CompanyListDTO, etc) in the most >>> > >> efficient way is >>> > >> > going to require very different SQL for each DTO. This >>> > >> implies some kind >>> > >> > of "mapping" to be able associate each DTO with query. >>> > >> > >>> > >> > Given 6.0's improved dynamic-instantiation support, I >>> even >>> > >> think that is a >>> > >> > great solution as well *for most cases*. >>> > >> > >>> > >> > So, while my objection has a "practical impact" >>> component, >>> > >> I also just >>> > >> > question whether Hibernate integrating with each format's >>> > >> "serializer" is >>> > >> > the proper solution. >>> > >> > >>> > >> > >>> > >> > >>> > >> > On Thu, May 4, 2017 at 5:08 AM Christian Beikov < >>> > >> > christian.beikov(a)gmail.com >>> > >> <mailto:christian.beikov@gmail.com>> wrote: >>> > >> > >>> > >> >> This is exactly what I am trying to do with >>> > >> Blaze-Persistence Entity >>> > >> >> Views, making DTOs sexy and efficient :) >>> > >> >> >>> > >> >> Here a quick overview of how that looks like right now: >>> > >> >> >>> > >> >> >>> > >> >>> > https://persistence.blazebit.com/documentation/entity-view/ >>> manual/en_US/index.html#first-entity-view-query >>> > >> < >>> > https://persistence.blazebit.com/documentation/entity-view/ >>> manual/en_US/index.html#first-entity-view-query >>> > > >>> > >> >> >>> > >> >> One of my targets is to make it possible to do something >>> > >> like this >>> > >> >> >>> > >> >> entityManager.createQuery("FROM Order o", >>> > >> OrderDTO.class).getResultList() >>> > >> >> >>> > >> >> and get an optimal query, as well as objects with only >>> the >>> > >> necessary >>> > >> >> contents. >>> > >> >> >>> > >> >> Maybe we can collaborate on that somehow? >>> > >> >> >>> > >> >> >>> > >> >> Mit freundlichen Grüßen, >>> > >> >> >>> > >> >>> > ------------------------------------------------------------ >>> ------------ >>> > >> >> *Christian Beikov* >>> > >> >> Am 04.05.2017 um 10:20 schrieb Emmanuel Bernard: >>> > >> >> > Following up a bit on my previous email. >>> > >> >> > >>> > >> >> > While a core integration might be best I think, if >>> there >>> > >> are too much >>> > >> >> > reluctance, we can start with a dedicated >>> hibernate-dto >>> > >> or whatever >>> > >> >> > module or even separate project that makes life easier >>> > >> for these "pass >>> > >> >> > through" use cases. This could be in the form of a >>> > >> wrapper API of sort >>> > >> >> > and hence not affect existing Hibernate ORM APIs. >>> > >> >> > >>> > >> >> > Note that the ResultTransformer approach feels like it >>> > >> goes a long way >>> > >> >> > towards fixing the problem but as demonstrated in >>> Vlad's >>> > >> article >>> > >> >> > >>> > >> >> >>> > >> >>> > https://vladmihalcea.com/2017/04/03/why-you-should-use-the- >>> hibernate-resulttransformer-to-customize-result-set-mappings/ >>> > >> < >>> > https://vladmihalcea.com/2017/04/03/why-you-should-use-the- >>> hibernate-resulttransformer-to-customize-result-set-mappings/ >>> > > >>> > >> >> > it still requires quite a bit of code and a special >>> DTO >>> > >> constructor >>> > >> >> > object. That's what we need to get rid of I think. >>> > >> >> > >>> > >> >> > Emmanuel >>> > >> >> > >>> > >> >> > On Thu 17-05-04 10:04, Emmanuel Bernard wrote: >>> > >> >> >> I was very much in the Vlad, Steve, Christian camp >>> > >> until relatively >>> > >> >> >> recently. One of my main concern being that >>> replacing a >>> > >> proxy by null >>> > >> >> >> was really sending the wrong message. So I was >>> against >>> > >> having Hibernate >>> > >> >> >> ORM facilitate such a transformation. >>> > >> >> >> >>> > >> >> >> I am changing my mind because I am realizing that a >>> lot >>> > >> of applications >>> > >> >> >> are less complex that my perceived median. A lot of >>> > >> apps really just >>> > >> >> >> want data to be fetched out and then passed to >>> jackson >>> > >> (implicitly) and >>> > >> >> >> pushed out as a REST response in JSON or some other >>> > >> serialization >>> > >> >> >> protocol. >>> > >> >> >> >>> > >> >> >> So while we could try and keep the stance that such a >>> > >> solution should >>> > >> >> >> remain out of scope of Hibernate ORM core, we should >>> > >> have a very smooth >>> > >> >> >> integration with something like MapStruct to create >>> > >> such bounded DTO on >>> > >> >> >> the fly. Ideally with as close to zero code as >>> possible >>> > >> from the user >>> > >> >> >> point of view. >>> > >> >> >> I can't really describe how that could look like >>> > >> because I am not >>> > >> >> >> familiar enough with MapStruct but I think it should >>> > >> have the following >>> > >> >> >> characteristics: >>> > >> >> >> >>> > >> >> >> 1. do an implicit binding between the mapped object >>> > >> graph and a >>> > >> >> detached >>> > >> >> >> object graph with a 1-1 mapping of type and >>> > >> replacing lazy objects >>> > >> >> and >>> > >> >> >> collections with null. That's the smoothest >>> approach >>> > >> and the most >>> > >> >> >> common use case but also the one where an >>> > >> inexperienced person could >>> > >> >> >> shoot at someone else's foot >>> > >> >> >> 2. do a binding between the mapped object graph and a >>> > >> detached version >>> > >> >> of >>> > >> >> >> that object graph with a 1-1 mapping of type, but >>> > >> declaratively >>> > >> >> >> expressing the boundaries for the detached >>> version. >>> > >> This enforces a >>> > >> >> >> clear thinking of the boundaries and will load >>> lazy >>> > >> data in case the >>> > >> >> >> object graph loaded is missing a bit. I like the >>> > >> idea on principle >>> > >> >> but >>> > >> >> >> I think it overlaps a lot with the fetch graph. >>> > >> >> >> 3. offer a full integration between MapStruct and >>> > >> Hibernate ORM by >>> > >> >> >> letting people express a full fledge MapStruct >>> > >> transformation >>> > >> >> between >>> > >> >> >> the managed object graph and a different target >>> > >> structure >>> > >> >> >> >>> > >> >> >> I favored MapStruct over Dozer because we know the >>> > >> MapStruct lead >>> > >> >> quite well ;) >>> > >> >> >> >>> > >> >> >> Note however that the MapStruct approach requires an >>> > >> explicit object >>> > >> >> >> copy, it feels a bit sad to have to double memory >>> > >> consumption. But that >>> > >> >> >> might be a good enough approach and bypassing the >>> > >> managed object >>> > >> >> >> creation leads to questions around the Persistence >>> > >> Context contract >>> > >> >> >> where loading an object supposedly means it will be >>> in >>> > >> the PC. >>> > >> >> >> Maybe a constructor like query syntax allowing to >>> > >> reference a MapStruct >>> > >> >> >> conversion logic might work? >>> > >> >> >> >>> > >> >> >> select mapStruct('order-and-items', o) from >>> Order o >>> > >> left join >>> > >> >> fetch o.items >>> > >> >> >> >>> > >> >> >> Emmanuel >>> > >> >> >> >>> > >> >> >> >>> > >> >> >> On Wed 17-04-19 14:29, Vlad Mihalcea wrote: >>> > >> >> >>> Hi, >>> > >> >> >>> >>> > >> >> >>> Although I keep on seeing this request from time to >>> > >> time, I still >>> > >> >> think >>> > >> >> >>> it's more like a Code Smell. >>> > >> >> >>> Entities are useful for when you plan to modify >>> them. >>> > >> Otherwise, a DTO >>> > >> >> >>> projection is much more efficient, and you don't >>> > >> suffer from >>> > >> >> >>> LazyInitializationException. >>> > >> >> >>> >>> > >> >> >>> With the ResultTransformer, you can even build >>> graphs >>> > >> of entities, as >>> > >> >> >>> explained in this article; >>> > >> >> >>> >>> > >> >> >>> >>> > >> >> >>> > >> >>> > https://vladmihalcea.com/2017/04/03/why-you-should-use-the- >>> hibernate-resulttransformer-to-customize-result-set-mappings/ >>> > >> < >>> > https://vladmihalcea.com/2017/04/03/why-you-should-use-the- >>> hibernate-resulttransformer-to-customize-result-set-mappings/ >>> > > >>> > >> >> >>> >>> > >> >> >>> Due to how Hibernate Proxies are handled, without >>> > Bytecode >>> > >> >> Enhancement, >>> > >> >> >>> it's difficult to replace a Proxy with null after >>> the >>> > >> Session is >>> > >> >> closed. If >>> > >> >> >>> we implemented this, we'd have to take into >>> > >> consideration both >>> > >> >> Javassist >>> > >> >> >>> and ByteBuddy as well as ByteCode Enhancements. >>> > >> >> >>> >>> > >> >> >>> all in all, the implementation effort might not >>> > >> justify the benefit, >>> > >> >> and >>> > >> >> >>> I'm skeptical of offering a feature that does not >>> > >> encourage data >>> > >> >> access >>> > >> >> >>> Best Practices. >>> > >> >> >>> >>> > >> >> >>> Vlad >>> > >> >> >>> >>> > >> >> >>> On Wed, Apr 19, 2017 at 2:18 PM, Christian Beikov < >>> > >> >> >>> christian.beikov(a)gmail.com >>> > >> <mailto:christian.beikov@gmail.com>> wrote: >>> > >> >> >>> >>> > >> >> >>>> Hey Romain, >>> > >> >> >>>> >>> > >> >> >>>> I don't think it is a good idea to expose entities >>> > >> directly if you >>> > >> >> >>>> really need a subset of the data. >>> > >> >> >>>> Reasons for that thinking are that it gets hard to >>> > >> define what needs >>> > >> >> to >>> > >> >> >>>> be fetched or is safe to be used for a particular >>> use >>> > >> case. Obviously >>> > >> >> >>>> serialization is like a follow-up problem. >>> > >> >> >>>> I see 2 possible solutions to the problem and both >>> > >> boil down to the >>> > >> >> use >>> > >> >> >>>> of DTOs. >>> > >> >> >>>> >>> > >> >> >>>> 1. Use an object mapper(e.g. Dozer) that maps >>> > >> entity object graphs >>> > >> >> to >>> > >> >> >>>> custom DTO types. >>> > >> >> >>>> 2. Use specialized DTOs in queries. >>> > >> >> >>>> >>> > >> >> >>>> >>> > >> >> >>>> Implementing 1. does not help you with lazy loading >>> > >> issues and 2. >>> > >> >> might >>> > >> >> >>>> require very intrusive changes in queries which is >>> > >> why I implemented >>> > >> >> >>>> Blaze-Persistence Entity Views >>> > >> >> >>>> >>> > >> <https://github.com/beikov/blaze-persistence#entity-view- >>> usage >>> > >> <https://github.com/beikov/blaze-persistence#entity-view- >>> usage >>> > >>. >>> > >> >> >>>> This is a library that allows you to define DTOs >>> with >>> > >> mappings to the >>> > >> >> >>>> entity. In a query you can define that you want >>> > >> results to be >>> > >> >> >>>> "materialized" as instances of the DTO type. >>> > >> >> >>>> This reduces the pain induced by properly >>> separating the >>> > >> >> "presentation >>> > >> >> >>>> model" from the "persistence model" and at the same >>> > >> time will improve >>> > >> >> >>>> the performance by utilizing the mapping >>> information. >>> > >> >> >>>> I don't want to advertise too much, just wanted to >>> > >> say that I had the >>> > >> >> >>>> same issues over and over which is why I started >>> that >>> > >> project. >>> > >> >> >>>> >>> > >> >> >>>> Mit freundlichen Grüßen, >>> > >> >> >>>> >>> > >> >> >>> > >> >>> > ------------------------------------------------------------ >>> ------------ >>> > >> >> >>>> *Christian Beikov* >>> > >> >> >>>> Am 19.04.2017 um 10:51 schrieb Romain Manni-Bucau: >>> > >> >> >>>>> Hi guys, >>> > >> >> >>>>> >>> > >> >> >>>>> Short sumarry: Wonder if hibernate could get a >>> > >> feature to kind of >>> > >> >> either >>> > >> >> >>>>> unproxy or freeze the entities once leaving the >>> > >> managed context to >>> > >> >> avoid >>> > >> >> >>>>> uncontrolled lazy loading on one side and >>> > >> serialization issues on >>> > >> >> another >>> > >> >> >>>>> side. >>> > >> >> >>>>> >>> > >> >> >>>>> Use case example: a common example is a REST >>> service >>> > >> exposing >>> > >> >> directly >>> > >> >> >>>>> hibernate entities (which is more and more common >>> > >> with microservice >>> > >> >> >>>>> "movement"). >>> > >> >> >>>>> >>> > >> >> >>>>> Objective: the goal is to not need any step - or >>> > >> reduce them a lot - >>> > >> >> >>>>> between the hibernate interaction and a potential >>> > >> serialization to >>> > >> >> avoid >>> > >> >> >>>>> issues with lazy loading and unexpected loading. >>> > >> Today it requires >>> > >> >> some >>> > >> >> >>>>> custom and hibernate specific logic in the >>> > >> serializer which kind of >>> > >> >> >>>> breaks >>> > >> >> >>>>> the transversality of the two concerns >>> > >> (serialization and object >>> > >> >> >>>>> management/loading). >>> > >> >> >>>>> >>> > >> >> >>>>> >>> > >> >> >>>>> Implementation options I see: >>> > >> >> >>>>> >>> > >> >> >>>>> 1. a callback requesting if the lazy relationship >>> > >> should be fetched, >>> > >> >> >>>>> something like >>> > >> >> >>>>> >>> > >> >> >>>>> public interface GraphVisitor { >>> > >> >> >>>>> boolean shouldLoad(Object rootEntity, >>> Property >>> > >> property); >>> > >> >> >>>>> } >>> > >> >> >>>>> >>> > >> >> >>>>> 2. An utility to remove any proxy potentially >>> > >> throwing an exception >>> > >> >> and >>> > >> >> >>>>> replacing the value by null or an empty >>> collection, >>> > >> something like >>> > >> >> >>>>> >>> > >> >> >>>>> MyEntity e = Hibernate.deepUnproxy(entity); >>> > >> >> >>>>> >>> > >> >> >>>>> 3. A switch of the proxy implementation, this is >>> > >> close to 2 but >>> > >> >> wouldn't >>> > >> >> >>>>> require a call to any utility, just a >>> configuration >>> > >> in the >>> > >> >> persistence >>> > >> >> >>>> unit. >>> > >> >> >>>>> Side note: of course all 3 options can be mixed to >>> > >> create a single >>> > >> >> >>>> solution >>> > >> >> >>>>> like having 3 implemented based on 1 for instance. >>> > >> >> >>>>> >>> > >> >> >>>>> Configuration proposal: this would be activated >>> > >> through a property >>> > >> >> in the >>> > >> >> >>>>> persistence unit (this shouldn't be only global >>> IMHO >>> > >> cause >>> > >> >> otherwise you >>> > >> >> >>>>> can't mix 2 kind of units, like one for JSF and >>> one >>> > >> for JAX-RS to be >>> > >> >> >>>>> concrete). This should also be activable as a >>> query >>> > >> hint i think - >>> > >> >> but >>> > >> >> >>>> more >>> > >> >> >>>>> a nice to have. >>> > >> >> >>>>> >>> > >> >> >>>>> >>> > >> >> >>>>> What this feature wouldn't be responsible for: >>> > >> cycles. If >>> > >> >> relationships >>> > >> >> >>>> are >>> > >> >> >>>>> bidirectional then the unproxied entity would >>> still >>> > >> "loop" if you >>> > >> >> browse >>> > >> >> >>>>> the object graph - this responsability would stay >>> in >>> > >> the consumer >>> > >> >> since >>> > >> >> >>>> it >>> > >> >> >>>>> doesn't depend on hibernate directly but more on a >>> > >> plain object >>> > >> >> handling. >>> > >> >> >>>>> >>> > >> >> >>>>> What do you think? >>> > >> >> >>>>> >>> > >> >> >>>>> >>> > >> >> >>>>> Romain Manni-Bucau >>> > >> >> >>>>> @rmannibucau <https://twitter.com/rmannibucau >>> > >> <https://twitter.com/rmannibucau>> | Blog >>> > >> >> >>>>> <https://blog-rmannibucau.rhcloud.com >>> > >> <https://blog-rmannibucau.rhcloud.com>> | Old Blog >>> > >> >> >>>>> <http://rmannibucau.wordpress.com >>> > >> <http://rmannibucau.wordpress.com>> | Github < >>> > https://github.com/ >>> > >> >> >>>> rmannibucau> | >>> > >> >> >>>>> LinkedIn <https://www.linkedin.com/in/rmannibucau >>> > >> <https://www.linkedin.com/in/rmannibucau>> | JavaEE >>> Factory >>> > >> >> >>>>> <https://javaeefactory-rmannibucau.rhcloud.com >>> > >> <https://javaeefactory-rmannibucau.rhcloud.com>> >>> > >> >> >>>>> _______________________________________________ >>> > >> >> >>>>> hibernate-dev mailing list >>> > >> >> >>>>> hibernate-dev(a)lists.jboss.org >>> > >> <mailto:hibernate-dev@lists.jboss.org> >>> > >> >> >>>>> >>> > >> https://lists.jboss.org/mailman/listinfo/hibernate-dev >>> > >> <https://lists.jboss.org/mailman/listinfo/hibernate-dev> >>> > >> >> >>>> _______________________________________________ >>> > >> >> >>>> hibernate-dev mailing list >>> > >> >> >>>> hibernate-dev(a)lists.jboss.org >>> > >> <mailto:hibernate-dev@lists.jboss.org> >>> > >> >> >>>> >>> > >> https://lists.jboss.org/mailman/listinfo/hibernate-dev >>> > >> <https://lists.jboss.org/mailman/listinfo/hibernate-dev> >>> > >> >> >>>> >>> > >> >> >>> _______________________________________________ >>> > >> >> >>> hibernate-dev mailing list >>> > >> >> >>> hibernate-dev(a)lists.jboss.org >>> > >> <mailto:hibernate-dev@lists.jboss.org> >>> > >> >> >>> https://lists.jboss.org/ >>> mailman/listinfo/hibernate-dev >>> > >> <https://lists.jboss.org/mailman/listinfo/hibernate-dev> >>> > >> >> >> _______________________________________________ >>> > >> >> >> hibernate-dev mailing list >>> > >> >> >> hibernate-dev(a)lists.jboss.org >>> > >> <mailto:hibernate-dev@lists.jboss.org> >>> > >> >> >> https://lists.jboss.org/ >>> mailman/listinfo/hibernate-dev >>> > >> <https://lists.jboss.org/mailman/listinfo/hibernate-dev> >>> > >> >> > _______________________________________________ >>> > >> >> > hibernate-dev mailing list >>> > >> >> > hibernate-dev(a)lists.jboss.org >>> > >> <mailto:hibernate-dev@lists.jboss.org> >>> > >> >> > https://lists.jboss.org/ >>> mailman/listinfo/hibernate-dev >>> > >> <https://lists.jboss.org/mailman/listinfo/hibernate-dev> >>> > >> >> >>> > >> >> _______________________________________________ >>> > >> >> hibernate-dev mailing list >>> > >> >> hibernate-dev(a)lists.jboss.org >>> > >> <mailto:hibernate-dev@lists.jboss.org> >>> > >> >> https://lists.jboss.org/mailman/listinfo/hibernate-dev >>> > >> <https://lists.jboss.org/mailman/listinfo/hibernate-dev> >>> > >> >> >>> > >> > >>> > >> _______________________________________________ >>> > >> hibernate-dev mailing list >>> > >> hibernate-dev(a)lists.jboss.org >>> > >> <mailto:hibernate-dev@lists.jboss.org> >>> > >> https://lists.jboss.org/mailman/listinfo/hibernate-dev >>> > >> <https://lists.jboss.org/mailman/listinfo/hibernate-dev> >>> > >> >>> > > >>> > > >>> > >>> > _______________________________________________ >>> > hibernate-dev mailing list >>> > hibernate-dev(a)lists.jboss.org >>> > https://lists.jboss.org/mailman/listinfo/hibernate-dev >>> _______________________________________________ >>> hibernate-dev mailing list >>> hibernate-dev(a)lists.jboss.org >>> https://lists.jboss.org/mailman/listinfo/hibernate-dev >>> >> >> >>

Hibernate#isInitialized is an overloaded method. I think you want to look at the different forms. And yes, Navigable will define visitor-based navigation. Hence the name ;) On Thu, May 4, 2017, 12:18 PM Romain Manni-Bucau <rmannibucau(a)gmail.com&gt; wrote: > 2017-05-04 19:16 GMT+02:00 Steve Ebersole <steve(a)hibernate.org&gt;: > >> But your psuedo code is really just the same as: >> >> AnEntity e = find(); >> if ( isInitialized( e ) ) { >> serializer.serialize(e); >> } >> > > no cause it is done in the graph visitor and not just the root, that's > the key difference. > > >> >> boolean isInitialized(Object e) { >> return Hibernate.isInitialized( e ); >> } >> >> What I was getting at with the 6.0 + Navigavble discussion is that it >> would be better to base this "isInitialized" on these Navigables instead. >> A Navigable is a polymorphic reference that might be an entity, a >> persistent attribute, a "collection element", etc. >> > > Would need to see it in a more concrete version but sounds tempting, > would it integrate a visitor - handling cycles? > > >> >> >> On Thu, May 4, 2017 at 11:46 AM Romain Manni-Bucau < >> rmannibucau(a)gmail.com&gt; wrote: >> >>> 2017-05-04 18:42 GMT+02:00 Christian Beikov <christian.beikov(a)gmail.com >>> >: >>> >>>> Detecting if an object is initialized should be as easy as calling " >>>> Hibernate.isInitialized(object)". If you want to know whether a >>>> specic attribute of an object is initialized you'd use "Hibernate.isPropertyInitialized(object, >>>> attributeName)". What you want is some kind of integration that makes >>>> use of these two methods, so that if they return false, a null value is >>>> used when serializing objects to XML/JSON via JAXB/JSONB. Is that correct? >>>> >>> >>> Almost, I would like one able to just disable it, this way the >>> serializer doesnt need anything or knowledge of hibernate. Worse case we >>> need to integrate with the serializer in a way close to the one i proposed >>> for johnzon before. >>> >>> In pseudo code it would be: >>> >>> AnEntity e = find(); >>> Hibernate.disableLazyExceptionWithNull(e); >>> serializer.serialize(e); >>> >>> >>>> I don't know of any hook in JAXB that could be used to put that code >>>> into so it works out as you'd expect it. The only other way I can think of, >>>> is nulling the properties explicitly which could be done quite easily. You >>>> probably gonna need just a single recursive method to do that. I don't see >>>> how that method should be part of Hibernate nor how you'd expect to be able >>>> to configure Hibernate so that it would do that transparently. >>>> >>> the switch of lazyexception to null would work wit jaxb. Otherwise you >>> need some more low level integration not portable IIRC. >>> >>> >>>> I still think the cleanest solution would be to have DTOs, which is >>>> why I'd argue that such a halve solution shouldn't be part of Hibernate. >>>> >>> >>> Think we all agree (or agreed already ;)) but created this thread cause >>> i saw it often enough to be a need. >>> >>> >>>> >>>> Mit freundlichen Grüßen, >>>> ------------------------------ >>>> *Christian Beikov* >>>> Am 04.05.2017 um 18:00 schrieb Romain Manni-Bucau: >>>> >>>> >>>> >>>> 2017-05-04 17:33 GMT+02:00 Steve Ebersole <steve(a)hibernate.org&gt;: >>>> >>>>> What exactly would this "utility one level further than existing >>>>> ones" do? >>>>> >>>>> >>>> Multiple options are possible but one is to return null instead of >>>> throwing lazy exception for instance. >>>> >>>> >>>>> And for what it is worth, IMO the new Navigable model in 6.0 will >>>>> again >>>>> help here. Especially in conjunction with the Navigable visitation >>>>> support. >>>>> >>>> >>>> I'm not familiar enough but if it providers for each member a way to >>>> know if it is loaded or not it can work. >>>> >>>> >>>>> >>>>> On Thu, May 4, 2017 at 10:27 AM Christian Beikov < >>>>> christian.beikov(a)gmail.com&gt; >>>>> wrote: >>>>> >>>>> > Well that is again exactly what a DTO is good for. If you as >>>>> developer >>>>> > want the groups to be available, you add a list of groups to that >>>>> > special DTO type for that use case. In your data access layer you >>>>> > somehow populate that, which is normally done by using some mapper >>>>> > library like MapStruct or Dozer and then JAXB/JSONB can just work >>>>> with >>>>> > the DTO type without any problems. >>>>> > >>>>> > Now if you forget to add a JOIN FETCH to your query and you end up >>>>> with >>>>> > N+1 queries, that's a different problem, just like the amount of >>>>> > boilerplate code needed for having DTO types for every use case. >>>>> That I >>>>> > try to solve with Blaze-Persistence Entity Views. >>>>> > >>>>> > Just a quick example to make my point here. If you have a REST >>>>> endpoint >>>>> > /user/{id} and want to provide the list of group names along with >>>>> the >>>>> > user information, you'd create a UserInfoDTO. >>>>> > >>>>> > @EntityView(User.class) >>>>> > interface UserInfoDTO { >>>>> > String getUsername(); >>>>> > @Mapping("groups.name") >>>>> > List<String> getGroups(); >>>>> > } >>>>> > >>>>> > Your repository returns an object of that type and you just pass >>>>> that >>>>> > object through so JAXB/JSONB can do their work. The mapping >>>>> information >>>>> > in the DTO is applied on a "source query" i.e. only doing the work >>>>> > absolutely necessary to satisfy the requested projection. >>>>> > >>>>> > Implementing this by hand is by no means impossible, but rather >>>>> > inconvenient I'd say, which is probably why you are seeking for >>>>> other >>>>> > solutions. >>>>> > >>>>> > In the end, you can only try to create a minimal DTO that has >>>>> exactly >>>>> > the fields you want to be serialized or annotate your existing >>>>> entities >>>>> > with those "ignore" annotations and hope for the best. I don't see >>>>> how >>>>> > hibernate could or should help in any of the two cases. >>>>> > >>>>> > Mit freundlichen Grüßen, >>>>> > >>>>> ------------------------------------------------------------------------ >>>>> > *Christian Beikov* >>>>> > Am 04.05.2017 um 16:59 schrieb Romain Manni-Bucau: >>>>> > > Sure. If you add any conversion logic then you are clearly out of >>>>> > > hibernate scope and the problem doesnt appear anymore. Here is a >>>>> > > trivial example (hopefully trivial at least ;)) >>>>> > > >>>>> > > User 1 - n Group >>>>> > > >>>>> > > In json we would get something like {username:...,groups:[group1, >>>>> > > group2]}, no issue to know if group should be loaded or not since >>>>> this >>>>> > > part of the logic is in the mapper layer. >>>>> > > >>>>> > > So yes you can say "not my problem" but next framework will >>>>> > > immediately ask "how do i know" and you likely end like all >>>>> > > spring-data-rest recommandation with a specific mapping and not a >>>>> > > framework solution which is the target of that thread - at least >>>>> what >>>>> > > I tried to explain ;). >>>>> > > >>>>> > > 2017-05-04 16:41 GMT+02:00 Christian Beikov >>>>> > > <christian.beikov(a)gmail.com <mailto:christian.beikov@gmail.com>>: >>>>> > > >>>>> > > I don't understand what you mean by "you put that logic in the >>>>> > > conversion", could you elaborate? >>>>> > > >>>>> > > >>>>> > > Mit freundlichen Grüßen, >>>>> > > >>>>> > >>>>> ------------------------------------------------------------------------ >>>>> > > *Christian Beikov* >>>>> > > Am 04.05.2017 um 16:32 schrieb Romain Manni-Bucau: >>>>> > >> Few more points: >>>>> > >> >>>>> > >> 1. Dto dont help at any moment - or you put that logic in the >>>>> > >> conversion and you are back to start >>>>> > >> 2. Making jaxb/jsonb easy to integrate is the goal IMO. No >>>>> need >>>>> > >> to integrate with them but just provide some utility one >>>>> level >>>>> > >> further than existing ones >>>>> > >> >>>>> > >> Le 4 mai 2017 16:13, "Steve Ebersole" <steve(a)hibernate.org >>>>> > >> <mailto:steve@hibernate.org>> a écrit : >>>>> > >> >>>>> > >> Oops, that (3) in previous reply should have read: >>>>> > >> 3. supporting each format creates a new "optional" >>>>> library >>>>> > >> dependency >>>>> > >> >>>>> > >> Overall, I like Christian's approach as a potential >>>>> > >> generalized approach to >>>>> > >> this. Basically a combination of >>>>> > >> >>>>> > >> 1. a query used to provide the "view source values" >>>>> > >> 2. some indication of how to map those "source >>>>> values" to >>>>> > >> your view model >>>>> > >> >>>>> > >> >>>>> > >> And again, I think 6.0's improved dynamic-instantiation >>>>> > >> queries are a >>>>> > >> simple, already-built-in way to achieve that for most >>>>> cases. >>>>> > >> But I am open >>>>> > >> to discussing a way to supply that combination via API >>>>> if we >>>>> > >> deem that >>>>> > >> would be good - although then I'd also question how the >>>>> current >>>>> > >> TupleTransformer does not meet that need. >>>>> > >> >>>>> > >> On Thu, May 4, 2017 at 8:43 AM Steve Ebersole >>>>> > >> <steve(a)hibernate.org <mailto:steve@hibernate.org>> >>>>> wrote: >>>>> > >> >>>>> > >> > Were there a standard "represent something in XML-ish >>>>> > >> format" contract >>>>> > >> > portable across a number of formats (XML, JAXB, JSON, >>>>> etc) >>>>> > >> then I'd be more >>>>> > >> > inclined to agree with this. But as it is, supporting >>>>> this >>>>> > >> would mean >>>>> > >> > Hibernate implementing multiple such contracts, one per >>>>> > >> format. However, >>>>> > >> > >>>>> > >> > 1. these formats are not our core competency >>>>> > >> > 2. maintaining a complete set of these transformers >>>>> > >> across all the >>>>> > >> > popular formats du-jour is a large undertaking >>>>> > >> > 3. I am not convinced that >>>>> > >> > >>>>> > >> > All of these increase the technical risk. >>>>> > >> > >>>>> > >> > Additionally, to properly support this we'd really >>>>> need the >>>>> > >> ability to >>>>> > >> > then "map" multiple views for a given >>>>> entity-graph-root. >>>>> > >> What I mean by >>>>> > >> > that, is that such DTO approaches often need multiple >>>>> > >> "views" of a given >>>>> > >> > entity, e.g. a CompanyListDTO, CompanyOverviewDTO, >>>>> > >> > CompanyDetailsGeneralDTO, etc for a Company entity. >>>>> The >>>>> > >> point of this is >>>>> > >> > that >>>>> > >> > >>>>> > >> > 1. the transformers for these are specific to each >>>>> DTO >>>>> > >> type and would >>>>> > >> > be applied per-transformation >>>>> > >> > 2. were Hibernate to "provide" this for applications >>>>> > >> > >>>>> > >> > IMO the use of queries to obtain views is logical. >>>>> > >> Populating each of >>>>> > >> > those specific DTOs (CompanyListDTO, etc) in the most >>>>> > >> efficient way is >>>>> > >> > going to require very different SQL for each DTO. This >>>>> > >> implies some kind >>>>> > >> > of "mapping" to be able associate each DTO with query. >>>>> > >> > >>>>> > >> > Given 6.0's improved dynamic-instantiation support, I >>>>> even >>>>> > >> think that is a >>>>> > >> > great solution as well *for most cases*. >>>>> > >> > >>>>> > >> > So, while my objection has a "practical impact" >>>>> component, >>>>> > >> I also just >>>>> > >> > question whether Hibernate integrating with each >>>>> format's >>>>> > >> "serializer" is >>>>> > >> > the proper solution. >>>>> > >> > >>>>> > >> > >>>>> > >> > >>>>> > >> > On Thu, May 4, 2017 at 5:08 AM Christian Beikov < >>>>> > >> > christian.beikov(a)gmail.com >>>>> > >> <mailto:christian.beikov@gmail.com>> wrote: >>>>> > >> > >>>>> > >> >> This is exactly what I am trying to do with >>>>> > >> Blaze-Persistence Entity >>>>> > >> >> Views, making DTOs sexy and efficient :) >>>>> > >> >> >>>>> > >> >> Here a quick overview of how that looks like right >>>>> now: >>>>> > >> >> >>>>> > >> >> >>>>> > >> >>>>> > >>>>> https://persistence.blazebit.com/documentation/entity-view/manual/en_US/i... >>>>> > >> < >>>>> > >>>>> https://persistence.blazebit.com/documentation/entity-view/manual/en_US/i... >>>>> > > >>>>> > >> >> >>>>> > >> >> One of my targets is to make it possible to do >>>>> something >>>>> > >> like this >>>>> > >> >> >>>>> > >> >> entityManager.createQuery("FROM Order o", >>>>> > >> OrderDTO.class).getResultList() >>>>> > >> >> >>>>> > >> >> and get an optimal query, as well as objects with >>>>> only the >>>>> > >> necessary >>>>> > >> >> contents. >>>>> > >> >> >>>>> > >> >> Maybe we can collaborate on that somehow? >>>>> > >> >> >>>>> > >> >> >>>>> > >> >> Mit freundlichen Grüßen, >>>>> > >> >> >>>>> > >> >>>>> > >>>>> ------------------------------------------------------------------------ >>>>> > >> >> *Christian Beikov* >>>>> > >> >> Am 04.05.2017 um 10:20 schrieb Emmanuel Bernard: >>>>> > >> >> > Following up a bit on my previous email. >>>>> > >> >> > >>>>> > >> >> > While a core integration might be best I think, if >>>>> there >>>>> > >> are too much >>>>> > >> >> > reluctance, we can start with a dedicated >>>>> hibernate-dto >>>>> > >> or whatever >>>>> > >> >> > module or even separate project that makes life >>>>> easier >>>>> > >> for these "pass >>>>> > >> >> > through" use cases. This could be in the form of a >>>>> > >> wrapper API of sort >>>>> > >> >> > and hence not affect existing Hibernate ORM APIs. >>>>> > >> >> > >>>>> > >> >> > Note that the ResultTransformer approach feels like >>>>> it >>>>> > >> goes a long way >>>>> > >> >> > towards fixing the problem but as demonstrated in >>>>> Vlad's >>>>> > >> article >>>>> > >> >> > >>>>> > >> >> >>>>> > >> >>>>> > >>>>> https://vladmihalcea.com/2017/04/03/why-you-should-use-the-hibernate-resu... >>>>> > >> < >>>>> > >>>>> https://vladmihalcea.com/2017/04/03/why-you-should-use-the-hibernate-resu... >>>>> > > >>>>> > >> >> > it still requires quite a bit of code and a special >>>>> DTO >>>>> > >> constructor >>>>> > >> >> > object. That's what we need to get rid of I think. >>>>> > >> >> > >>>>> > >> >> > Emmanuel >>>>> > >> >> > >>>>> > >> >> > On Thu 17-05-04 10:04, Emmanuel Bernard wrote: >>>>> > >> >> >> I was very much in the Vlad, Steve, Christian camp >>>>> > >> until relatively >>>>> > >> >> >> recently. One of my main concern being that >>>>> replacing a >>>>> > >> proxy by null >>>>> > >> >> >> was really sending the wrong message. So I was >>>>> against >>>>> > >> having Hibernate >>>>> > >> >> >> ORM facilitate such a transformation. >>>>> > >> >> >> >>>>> > >> >> >> I am changing my mind because I am realizing that >>>>> a lot >>>>> > >> of applications >>>>> > >> >> >> are less complex that my perceived median. A lot of >>>>> > >> apps really just >>>>> > >> >> >> want data to be fetched out and then passed to >>>>> jackson >>>>> > >> (implicitly) and >>>>> > >> >> >> pushed out as a REST response in JSON or some other >>>>> > >> serialization >>>>> > >> >> >> protocol. >>>>> > >> >> >> >>>>> > >> >> >> So while we could try and keep the stance that >>>>> such a >>>>> > >> solution should >>>>> > >> >> >> remain out of scope of Hibernate ORM core, we >>>>> should >>>>> > >> have a very smooth >>>>> > >> >> >> integration with something like MapStruct to create >>>>> > >> such bounded DTO on >>>>> > >> >> >> the fly. Ideally with as close to zero code as >>>>> possible >>>>> > >> from the user >>>>> > >> >> >> point of view. >>>>> > >> >> >> I can't really describe how that could look like >>>>> > >> because I am not >>>>> > >> >> >> familiar enough with MapStruct but I think it >>>>> should >>>>> > >> have the following >>>>> > >> >> >> characteristics: >>>>> > >> >> >> >>>>> > >> >> >> 1. do an implicit binding between the mapped object >>>>> > >> graph and a >>>>> > >> >> detached >>>>> > >> >> >> object graph with a 1-1 mapping of type and >>>>> > >> replacing lazy objects >>>>> > >> >> and >>>>> > >> >> >> collections with null. That's the smoothest >>>>> approach >>>>> > >> and the most >>>>> > >> >> >> common use case but also the one where an >>>>> > >> inexperienced person could >>>>> > >> >> >> shoot at someone else's foot >>>>> > >> >> >> 2. do a binding between the mapped object graph >>>>> and a >>>>> > >> detached version >>>>> > >> >> of >>>>> > >> >> >> that object graph with a 1-1 mapping of type, >>>>> but >>>>> > >> declaratively >>>>> > >> >> >> expressing the boundaries for the detached >>>>> version. >>>>> > >> This enforces a >>>>> > >> >> >> clear thinking of the boundaries and will load >>>>> lazy >>>>> > >> data in case the >>>>> > >> >> >> object graph loaded is missing a bit. I like the >>>>> > >> idea on principle >>>>> > >> >> but >>>>> > >> >> >> I think it overlaps a lot with the fetch graph. >>>>> > >> >> >> 3. offer a full integration between MapStruct and >>>>> > >> Hibernate ORM by >>>>> > >> >> >> letting people express a full fledge MapStruct >>>>> > >> transformation >>>>> > >> >> between >>>>> > >> >> >> the managed object graph and a different target >>>>> > >> structure >>>>> > >> >> >> >>>>> > >> >> >> I favored MapStruct over Dozer because we know the >>>>> > >> MapStruct lead >>>>> > >> >> quite well ;) >>>>> > >> >> >> >>>>> > >> >> >> Note however that the MapStruct approach requires >>>>> an >>>>> > >> explicit object >>>>> > >> >> >> copy, it feels a bit sad to have to double memory >>>>> > >> consumption. But that >>>>> > >> >> >> might be a good enough approach and bypassing the >>>>> > >> managed object >>>>> > >> >> >> creation leads to questions around the Persistence >>>>> > >> Context contract >>>>> > >> >> >> where loading an object supposedly means it will >>>>> be in >>>>> > >> the PC. >>>>> > >> >> >> Maybe a constructor like query syntax allowing to >>>>> > >> reference a MapStruct >>>>> > >> >> >> conversion logic might work? >>>>> > >> >> >> >>>>> > >> >> >> select mapStruct('order-and-items', o) from >>>>> Order o >>>>> > >> left join >>>>> > >> >> fetch o.items >>>>> > >> >> >> >>>>> > >> >> >> Emmanuel >>>>> > >> >> >> >>>>> > >> >> >> >>>>> > >> >> >> On Wed 17-04-19 14:29, Vlad Mihalcea wrote: >>>>> > >> >> >>> Hi, >>>>> > >> >> >>> >>>>> > >> >> >>> Although I keep on seeing this request from time >>>>> to >>>>> > >> time, I still >>>>> > >> >> think >>>>> > >> >> >>> it's more like a Code Smell. >>>>> > >> >> >>> Entities are useful for when you plan to modify >>>>> them. >>>>> > >> Otherwise, a DTO >>>>> > >> >> >>> projection is much more efficient, and you don't >>>>> > >> suffer from >>>>> > >> >> >>> LazyInitializationException. >>>>> > >> >> >>> >>>>> > >> >> >>> With the ResultTransformer, you can even build >>>>> graphs >>>>> > >> of entities, as >>>>> > >> >> >>> explained in this article; >>>>> > >> >> >>> >>>>> > >> >> >>> >>>>> > >> >> >>>>> > >> >>>>> > >>>>> https://vladmihalcea.com/2017/04/03/why-you-should-use-the-hibernate-resu... >>>>> > >> < >>>>> > >>>>> https://vladmihalcea.com/2017/04/03/why-you-should-use-the-hibernate-resu... >>>>> > > >>>>> > >> >> >>> >>>>> > >> >> >>> Due to how Hibernate Proxies are handled, without >>>>> > Bytecode >>>>> > >> >> Enhancement, >>>>> > >> >> >>> it's difficult to replace a Proxy with null after >>>>> the >>>>> > >> Session is >>>>> > >> >> closed. If >>>>> > >> >> >>> we implemented this, we'd have to take into >>>>> > >> consideration both >>>>> > >> >> Javassist >>>>> > >> >> >>> and ByteBuddy as well as ByteCode Enhancements. >>>>> > >> >> >>> >>>>> > >> >> >>> all in all, the implementation effort might not >>>>> > >> justify the benefit, >>>>> > >> >> and >>>>> > >> >> >>> I'm skeptical of offering a feature that does not >>>>> > >> encourage data >>>>> > >> >> access >>>>> > >> >> >>> Best Practices. >>>>> > >> >> >>> >>>>> > >> >> >>> Vlad >>>>> > >> >> >>> >>>>> > >> >> >>> On Wed, Apr 19, 2017 at 2:18 PM, Christian Beikov >>>>> < >>>>> > >> >> >>> christian.beikov(a)gmail.com >>>>> > >> <mailto:christian.beikov@gmail.com>> wrote: >>>>> > >> >> >>> >>>>> > >> >> >>>> Hey Romain, >>>>> > >> >> >>>> >>>>> > >> >> >>>> I don't think it is a good idea to expose >>>>> entities >>>>> > >> directly if you >>>>> > >> >> >>>> really need a subset of the data. >>>>> > >> >> >>>> Reasons for that thinking are that it gets hard >>>>> to >>>>> > >> define what needs >>>>> > >> >> to >>>>> > >> >> >>>> be fetched or is safe to be used for a >>>>> particular use >>>>> > >> case. Obviously >>>>> > >> >> >>>> serialization is like a follow-up problem. >>>>> > >> >> >>>> I see 2 possible solutions to the problem and >>>>> both >>>>> > >> boil down to the >>>>> > >> >> use >>>>> > >> >> >>>> of DTOs. >>>>> > >> >> >>>> >>>>> > >> >> >>>> 1. Use an object mapper(e.g. Dozer) that maps >>>>> > >> entity object graphs >>>>> > >> >> to >>>>> > >> >> >>>> custom DTO types. >>>>> > >> >> >>>> 2. Use specialized DTOs in queries. >>>>> > >> >> >>>> >>>>> > >> >> >>>> >>>>> > >> >> >>>> Implementing 1. does not help you with lazy >>>>> loading >>>>> > >> issues and 2. >>>>> > >> >> might >>>>> > >> >> >>>> require very intrusive changes in queries which >>>>> is >>>>> > >> why I implemented >>>>> > >> >> >>>> Blaze-Persistence Entity Views >>>>> > >> >> >>>> >>>>> > >> < >>>>> https://github.com/beikov/blaze-persistence#entity-view-usage >>>>> > >> < >>>>> https://github.com/beikov/blaze-persistence#entity-view-usage >>>>> > >>. >>>>> > >> >> >>>> This is a library that allows you to define DTOs >>>>> with >>>>> > >> mappings to the >>>>> > >> >> >>>> entity. In a query you can define that you want >>>>> > >> results to be >>>>> > >> >> >>>> "materialized" as instances of the DTO type. >>>>> > >> >> >>>> This reduces the pain induced by properly >>>>> separating the >>>>> > >> >> "presentation >>>>> > >> >> >>>> model" from the "persistence model" and at the >>>>> same >>>>> > >> time will improve >>>>> > >> >> >>>> the performance by utilizing the mapping >>>>> information. >>>>> > >> >> >>>> I don't want to advertise too much, just wanted >>>>> to >>>>> > >> say that I had the >>>>> > >> >> >>>> same issues over and over which is why I started >>>>> that >>>>> > >> project. >>>>> > >> >> >>>> >>>>> > >> >> >>>> Mit freundlichen Grüßen, >>>>> > >> >> >>>> >>>>> > >> >> >>>>> > >> >>>>> > >>>>> ------------------------------------------------------------------------ >>>>> > >> >> >>>> *Christian Beikov* >>>>> > >> >> >>>> Am 19.04.2017 um 10:51 schrieb Romain >>>>> Manni-Bucau: >>>>> > >> >> >>>>> Hi guys, >>>>> > >> >> >>>>> >>>>> > >> >> >>>>> Short sumarry: Wonder if hibernate could get a >>>>> > >> feature to kind of >>>>> > >> >> either >>>>> > >> >> >>>>> unproxy or freeze the entities once leaving the >>>>> > >> managed context to >>>>> > >> >> avoid >>>>> > >> >> >>>>> uncontrolled lazy loading on one side and >>>>> > >> serialization issues on >>>>> > >> >> another >>>>> > >> >> >>>>> side. >>>>> > >> >> >>>>> >>>>> > >> >> >>>>> Use case example: a common example is a REST >>>>> service >>>>> > >> exposing >>>>> > >> >> directly >>>>> > >> >> >>>>> hibernate entities (which is more and more >>>>> common >>>>> > >> with microservice >>>>> > >> >> >>>>> "movement"). >>>>> > >> >> >>>>> >>>>> > >> >> >>>>> Objective: the goal is to not need any step - or >>>>> > >> reduce them a lot - >>>>> > >> >> >>>>> between the hibernate interaction and a >>>>> potential >>>>> > >> serialization to >>>>> > >> >> avoid >>>>> > >> >> >>>>> issues with lazy loading and unexpected loading. >>>>> > >> Today it requires >>>>> > >> >> some >>>>> > >> >> >>>>> custom and hibernate specific logic in the >>>>> > >> serializer which kind of >>>>> > >> >> >>>> breaks >>>>> > >> >> >>>>> the transversality of the two concerns >>>>> > >> (serialization and object >>>>> > >> >> >>>>> management/loading). >>>>> > >> >> >>>>> >>>>> > >> >> >>>>> >>>>> > >> >> >>>>> Implementation options I see: >>>>> > >> >> >>>>> >>>>> > >> >> >>>>> 1. a callback requesting if the lazy >>>>> relationship >>>>> > >> should be fetched, >>>>> > >> >> >>>>> something like >>>>> > >> >> >>>>> >>>>> > >> >> >>>>> public interface GraphVisitor { >>>>> > >> >> >>>>> boolean shouldLoad(Object rootEntity, >>>>> Property >>>>> > >> property); >>>>> > >> >> >>>>> } >>>>> > >> >> >>>>> >>>>> > >> >> >>>>> 2. An utility to remove any proxy potentially >>>>> > >> throwing an exception >>>>> > >> >> and >>>>> > >> >> >>>>> replacing the value by null or an empty >>>>> collection, >>>>> > >> something like >>>>> > >> >> >>>>> >>>>> > >> >> >>>>> MyEntity e = Hibernate.deepUnproxy(entity); >>>>> > >> >> >>>>> >>>>> > >> >> >>>>> 3. A switch of the proxy implementation, this is >>>>> > >> close to 2 but >>>>> > >> >> wouldn't >>>>> > >> >> >>>>> require a call to any utility, just a >>>>> configuration >>>>> > >> in the >>>>> > >> >> persistence >>>>> > >> >> >>>> unit. >>>>> > >> >> >>>>> Side note: of course all 3 options can be mixed >>>>> to >>>>> > >> create a single >>>>> > >> >> >>>> solution >>>>> > >> >> >>>>> like having 3 implemented based on 1 for >>>>> instance. >>>>> > >> >> >>>>> >>>>> > >> >> >>>>> Configuration proposal: this would be activated >>>>> > >> through a property >>>>> > >> >> in the >>>>> > >> >> >>>>> persistence unit (this shouldn't be only global >>>>> IMHO >>>>> > >> cause >>>>> > >> >> otherwise you >>>>> > >> >> >>>>> can't mix 2 kind of units, like one for JSF and >>>>> one >>>>> > >> for JAX-RS to be >>>>> > >> >> >>>>> concrete). This should also be activable as a >>>>> query >>>>> > >> hint i think - >>>>> > >> >> but >>>>> > >> >> >>>> more >>>>> > >> >> >>>>> a nice to have. >>>>> > >> >> >>>>> >>>>> > >> >> >>>>> >>>>> > >> >> >>>>> What this feature wouldn't be responsible for: >>>>> > >> cycles. If >>>>> > >> >> relationships >>>>> > >> >> >>>> are >>>>> > >> >> >>>>> bidirectional then the unproxied entity would >>>>> still >>>>> > >> "loop" if you >>>>> > >> >> browse >>>>> > >> >> >>>>> the object graph - this responsability would >>>>> stay in >>>>> > >> the consumer >>>>> > >> >> since >>>>> > >> >> >>>> it >>>>> > >> >> >>>>> doesn't depend on hibernate directly but more >>>>> on a >>>>> > >> plain object >>>>> > >> >> handling. >>>>> > >> >> >>>>> >>>>> > >> >> >>>>> What do you think? >>>>> > >> >> >>>>> >>>>> > >> >> >>>>> >>>>> > >> >> >>>>> Romain Manni-Bucau >>>>> > >> >> >>>>> @rmannibucau <https://twitter.com/rmannibucau >>>>> > >> <https://twitter.com/rmannibucau>> | Blog >>>>> > >> >> >>>>> <https://blog-rmannibucau.rhcloud.com >>>>> > >> <https://blog-rmannibucau.rhcloud.com>> | Old Blog >>>>> > >> >> >>>>> <http://rmannibucau.wordpress.com >>>>> > >> <http://rmannibucau.wordpress.com>> | Github < >>>>> > https://github.com/ >>>>> > >> >> >>>> rmannibucau> | >>>>> > >> >> >>>>> LinkedIn < >>>>> https://www.linkedin.com/in/rmannibucau >>>>> > >> <https://www.linkedin.com/in/rmannibucau>> | JavaEE >>>>> Factory >>>>> > >> >> >>>>> <https://javaeefactory-rmannibucau.rhcloud.com >>>>> > >> <https://javaeefactory-rmannibucau.rhcloud.com>> >>>>> > >> >> >>>>> _______________________________________________ >>>>> > >> >> >>>>> hibernate-dev mailing list >>>>> > >> >> >>>>> hibernate-dev(a)lists.jboss.org >>>>> > >> <mailto:hibernate-dev@lists.jboss.org> >>>>> > >> >> >>>>> >>>>> > >> https://lists.jboss.org/mailman/listinfo/hibernate-dev >>>>> > >> <https://lists.jboss.org/mailman/listinfo/hibernate-dev> >>>>> > >> >> >>>> _______________________________________________ >>>>> > >> >> >>>> hibernate-dev mailing list >>>>> > >> >> >>>> hibernate-dev(a)lists.jboss.org >>>>> > >> <mailto:hibernate-dev@lists.jboss.org> >>>>> > >> >> >>>> >>>>> > >> https://lists.jboss.org/mailman/listinfo/hibernate-dev >>>>> > >> <https://lists.jboss.org/mailman/listinfo/hibernate-dev> >>>>> > >> >> >>>> >>>>> > >> >> >>> _______________________________________________ >>>>> > >> >> >>> hibernate-dev mailing list >>>>> > >> >> >>> hibernate-dev(a)lists.jboss.org >>>>> > >> <mailto:hibernate-dev@lists.jboss.org> >>>>> > >> >> >>> >>>>> https://lists.jboss.org/mailman/listinfo/hibernate-dev >>>>> > >> <https://lists.jboss.org/mailman/listinfo/hibernate-dev> >>>>> > >> >> >> _______________________________________________ >>>>> > >> >> >> hibernate-dev mailing list >>>>> > >> >> >> hibernate-dev(a)lists.jboss.org >>>>> > >> <mailto:hibernate-dev@lists.jboss.org> >>>>> > >> >> >> >>>>> https://lists.jboss.org/mailman/listinfo/hibernate-dev >>>>> > >> <https://lists.jboss.org/mailman/listinfo/hibernate-dev> >>>>> > >> >> > _______________________________________________ >>>>> > >> >> > hibernate-dev mailing list >>>>> > >> >> > hibernate-dev(a)lists.jboss.org >>>>> > >> <mailto:hibernate-dev@lists.jboss.org> >>>>> > >> >> > >>>>> https://lists.jboss.org/mailman/listinfo/hibernate-dev >>>>> > >> <https://lists.jboss.org/mailman/listinfo/hibernate-dev> >>>>> > >> >> >>>>> > >> >> _______________________________________________ >>>>> > >> >> hibernate-dev mailing list >>>>> > >> >> hibernate-dev(a)lists.jboss.org >>>>> > >> <mailto:hibernate-dev@lists.jboss.org> >>>>> > >> >> >>>>> https://lists.jboss.org/mailman/listinfo/hibernate-dev >>>>> > >> <https://lists.jboss.org/mailman/listinfo/hibernate-dev> >>>>> > >> >> >>>>> > >> > >>>>> > >> _______________________________________________ >>>>> > >> hibernate-dev mailing list >>>>> > >> hibernate-dev(a)lists.jboss.org >>>>> > >> <mailto:hibernate-dev@lists.jboss.org> >>>>> > >> https://lists.jboss.org/mailman/listinfo/hibernate-dev >>>>> > >> <https://lists.jboss.org/mailman/listinfo/hibernate-dev> >>>>> > >> >>>>> > > >>>>> > > >>>>> > >>>>> > _______________________________________________ >>>>> > hibernate-dev mailing list >>>>> > hibernate-dev(a)lists.jboss.org >>>>> > https://lists.jboss.org/mailman/listinfo/hibernate-dev >>>>> _______________________________________________ >>>>> hibernate-dev mailing list >>>>> hibernate-dev(a)lists.jboss.org >>>>> https://lists.jboss.org/mailman/listinfo/hibernate-dev >>>>> >>>> >>>> >>>>

2017-05-04 19:28 GMT+02:00 Steve Ebersole <steve(a)hibernate.org&gt;: > I should clarify... if your `serialzer#serialize` call is not > "recursively" calling into this check then my example would not work; but > then again, neither would yours > Well mine works (no "would" ;)) cause jsonb implements the visitor pattern for me in my case. But ok, let's see this Navigable solution when out, sounds promishing. > > On Thu, May 4, 2017, 12:26 PM Steve Ebersole <steve(a)hibernate.org&gt; wrote: > >> Hibernate#isInitialized is an overloaded method. I think you want to >> look at the different forms. >> >> And yes, Navigable will define visitor-based navigation. Hence the name ;) >> >> On Thu, May 4, 2017, 12:18 PM Romain Manni-Bucau <rmannibucau(a)gmail.com > >> wrote: >> >>> 2017-05-04 19:16 GMT+02:00 Steve Ebersole <steve(a)hibernate.org&gt;: >>> >>>> But your psuedo code is really just the same as: >>>> >>>> AnEntity e = find(); >>>> if ( isInitialized( e ) ) { >>>> serializer.serialize(e); >>>> } >>>> >>> >>> no cause it is done in the graph visitor and not just the root, that's >>> the key difference. >>> >>> >>>> >>>> boolean isInitialized(Object e) { >>>> return Hibernate.isInitialized( e ); >>>> } >>>> >>>> What I was getting at with the 6.0 + Navigavble discussion is that it >>>> would be better to base this "isInitialized" on these Navigables instead. >>>> A Navigable is a polymorphic reference that might be an entity, a >>>> persistent attribute, a "collection element", etc. >>>> >>> >>> Would need to see it in a more concrete version but sounds tempting, >>> would it integrate a visitor - handling cycles? >>> >>> >>>> >>>> >>>> On Thu, May 4, 2017 at 11:46 AM Romain Manni-Bucau < >>>> rmannibucau(a)gmail.com&gt; wrote: >>>> >>>>> 2017-05-04 18:42 GMT+02:00 Christian Beikov < >>>>> christian.beikov(a)gmail.com&gt;: >>>>> >>>>>> Detecting if an object is initialized should be as easy as calling " >>>>>> Hibernate.isInitialized(object)". If you want to know whether a >>>>>> specic attribute of an object is initialized you'd use "Hibernate. isPropertyInitialized(object, >>>>>> attributeName)". What you want is some kind of integration that >>>>>> makes use of these two methods, so that if they return false, a null value >>>>>> is used when serializing objects to XML/JSON via JAXB/JSONB. Is that >>>>>> correct? >>>>>> >>>>> >>>>> Almost, I would like one able to just disable it, this way the >>>>> serializer doesnt need anything or knowledge of hibernate. Worse case we >>>>> need to integrate with the serializer in a way close to the one i proposed >>>>> for johnzon before. >>>>> >>>>> In pseudo code it would be: >>>>> >>>>> AnEntity e = find(); >>>>> Hibernate.disableLazyExceptionWithNull(e); >>>>> serializer.serialize(e); >>>>> >>>>> >>>>>> I don't know of any hook in JAXB that could be used to put that code >>>>>> into so it works out as you'd expect it. The only other way I can think of, >>>>>> is nulling the properties explicitly which could be done quite easily. You >>>>>> probably gonna need just a single recursive method to do that. I don't see >>>>>> how that method should be part of Hibernate nor how you'd expect to be able >>>>>> to configure Hibernate so that it would do that transparently. >>>>>> >>>>> the switch of lazyexception to null would work wit jaxb. Otherwise you >>>>> need some more low level integration not portable IIRC. >>>>> >>>>> >>>>>> I still think the cleanest solution would be to have DTOs, which is >>>>>> why I'd argue that such a halve solution shouldn't be part of Hibernate. >>>>>> >>>>> >>>>> Think we all agree (or agreed already ;)) but created this thread >>>>> cause i saw it often enough to be a need. >>>>> >>>>> >>>>>> >>>>>> Mit freundlichen Grüßen, >>>>>> ------------------------------ >>>>>> *Christian Beikov* >>>>>> Am 04.05.2017 um 18:00 schrieb Romain Manni-Bucau: >>>>>> >>>>>> >>>>>> >>>>>> 2017-05-04 17:33 GMT+02:00 Steve Ebersole <steve(a)hibernate.org&gt;: >>>>>> >>>>>>> What exactly would this "utility one level further than existing >>>>>>> ones" do? >>>>>>> >>>>>>> >>>>>> Multiple options are possible but one is to return null instead of >>>>>> throwing lazy exception for instance. >>>>>> >>>>>> >>>>>>> And for what it is worth, IMO the new Navigable model in 6.0 will >>>>>>> again >>>>>>> help here. Especially in conjunction with the Navigable visitation >>>>>>> support. >>>>>>> >>>>>> >>>>>> I'm not familiar enough but if it providers for each member a way to >>>>>> know if it is loaded or not it can work. >>>>>> >>>>>> >>>>>>> >>>>>>> On Thu, May 4, 2017 at 10:27 AM Christian Beikov < >>>>>>> christian.beikov(a)gmail.com&gt; >>>>>>> wrote: >>>>>>> >>>>>>> > Well that is again exactly what a DTO is good for. If you as >>>>>>> developer >>>>>>> > want the groups to be available, you add a list of groups to that >>>>>>> > special DTO type for that use case. In your data access layer you >>>>>>> > somehow populate that, which is normally done by using some mapper >>>>>>> > library like MapStruct or Dozer and then JAXB/JSONB can just work >>>>>>> with >>>>>>> > the DTO type without any problems. >>>>>>> > >>>>>>> > Now if you forget to add a JOIN FETCH to your query and you end up >>>>>>> with >>>>>>> > N+1 queries, that's a different problem, just like the amount of >>>>>>> > boilerplate code needed for having DTO types for every use case. >>>>>>> That I >>>>>>> > try to solve with Blaze-Persistence Entity Views. >>>>>>> > >>>>>>> > Just a quick example to make my point here. If you have a REST >>>>>>> endpoint >>>>>>> > /user/{id} and want to provide the list of group names along with >>>>>>> the >>>>>>> > user information, you'd create a UserInfoDTO. >>>>>>> > >>>>>>> > @EntityView(User.class) >>>>>>> > interface UserInfoDTO { >>>>>>> > String getUsername(); >>>>>>> > @Mapping("groups.name") >>>>>>> > List<String> getGroups(); >>>>>>> > } >>>>>>> > >>>>>>> > Your repository returns an object of that type and you just pass >>>>>>> that >>>>>>> > object through so JAXB/JSONB can do their work. The mapping >>>>>>> information >>>>>>> > in the DTO is applied on a "source query" i.e. only doing the work >>>>>>> > absolutely necessary to satisfy the requested projection. >>>>>>> > >>>>>>> > Implementing this by hand is by no means impossible, but rather >>>>>>> > inconvenient I'd say, which is probably why you are seeking for >>>>>>> other >>>>>>> > solutions. >>>>>>> > >>>>>>> > In the end, you can only try to create a minimal DTO that has >>>>>>> exactly >>>>>>> > the fields you want to be serialized or annotate your existing >>>>>>> entities >>>>>>> > with those "ignore" annotations and hope for the best. I don't see >>>>>>> how >>>>>>> > hibernate could or should help in any of the two cases. >>>>>>> > >>>>>>> > Mit freundlichen Grüßen, >>>>>>> > ------------------------------------------------------------ >>>>>>> ------------ >>>>>>> > *Christian Beikov* >>>>>>> > Am 04.05.2017 um 16:59 schrieb Romain Manni-Bucau: >>>>>>> > > Sure. If you add any conversion logic then you are clearly out of >>>>>>> > > hibernate scope and the problem doesnt appear anymore. Here is a >>>>>>> > > trivial example (hopefully trivial at least ;)) >>>>>>> > > >>>>>>> > > User 1 - n Group >>>>>>> > > >>>>>>> > > In json we would get something like {username:...,groups:[group1, >>>>>>> > > group2]}, no issue to know if group should be loaded or not >>>>>>> since this >>>>>>> > > part of the logic is in the mapper layer. >>>>>>> > > >>>>>>> > > So yes you can say "not my problem" but next framework will >>>>>>> > > immediately ask "how do i know" and you likely end like all >>>>>>> > > spring-data-rest recommandation with a specific mapping and not a >>>>>>> > > framework solution which is the target of that thread - at least >>>>>>> what >>>>>>> > > I tried to explain ;). >>>>>>> > > >>>>>>> > > 2017-05-04 16:41 GMT+02:00 Christian Beikov >>>>>>> > > <christian.beikov(a)gmail.com <mailto:christian.beikov@gmail.com >>>>>>> >>: >>>>>>> > > >>>>>>> > > I don't understand what you mean by "you put that logic in >>>>>>> the >>>>>>> > > conversion", could you elaborate? >>>>>>> > > >>>>>>> > > >>>>>>> > > Mit freundlichen Grüßen, >>>>>>> > > >>>>>>> > ------------------------------------------------------------ >>>>>>> ------------ >>>>>>> > > *Christian Beikov* >>>>>>> > > Am 04.05.2017 um 16:32 schrieb Romain Manni-Bucau: >>>>>>> > >> Few more points: >>>>>>> > >> >>>>>>> > >> 1. Dto dont help at any moment - or you put that logic in >>>>>>> the >>>>>>> > >> conversion and you are back to start >>>>>>> > >> 2. Making jaxb/jsonb easy to integrate is the goal IMO. No >>>>>>> need >>>>>>> > >> to integrate with them but just provide some utility one >>>>>>> level >>>>>>> > >> further than existing ones >>>>>>> > >> >>>>>>> > >> Le 4 mai 2017 16:13, "Steve Ebersole" < steve(a)hibernate.org >>>>>>> > >> <mailto:steve@hibernate.org>> a écrit : >>>>>>> > >> >>>>>>> > >> Oops, that (3) in previous reply should have read: >>>>>>> > >> 3. supporting each format creates a new "optional" >>>>>>> library >>>>>>> > >> dependency >>>>>>> > >> >>>>>>> > >> Overall, I like Christian's approach as a potential >>>>>>> > >> generalized approach to >>>>>>> > >> this. Basically a combination of >>>>>>> > >> >>>>>>> > >> 1. a query used to provide the "view source values" >>>>>>> > >> 2. some indication of how to map those "source >>>>>>> values" to >>>>>>> > >> your view model >>>>>>> > >> >>>>>>> > >> >>>>>>> > >> And again, I think 6.0's improved dynamic-instantiation >>>>>>> > >> queries are a >>>>>>> > >> simple, already-built-in way to achieve that for most >>>>>>> cases. >>>>>>> > >> But I am open >>>>>>> > >> to discussing a way to supply that combination via API >>>>>>> if we >>>>>>> > >> deem that >>>>>>> > >> would be good - although then I'd also question how the >>>>>>> current >>>>>>> > >> TupleTransformer does not meet that need. >>>>>>> > >> >>>>>>> > >> On Thu, May 4, 2017 at 8:43 AM Steve Ebersole >>>>>>> > >> <steve(a)hibernate.org <mailto:steve@hibernate.org>> >>>>>>> wrote: >>>>>>> > >> >>>>>>> > >> > Were there a standard "represent something in XML-ish >>>>>>> > >> format" contract >>>>>>> > >> > portable across a number of formats (XML, JAXB, JSON, >>>>>>> etc) >>>>>>> > >> then I'd be more >>>>>>> > >> > inclined to agree with this. But as it is, >>>>>>> supporting this >>>>>>> > >> would mean >>>>>>> > >> > Hibernate implementing multiple such contracts, one >>>>>>> per >>>>>>> > >> format. However, >>>>>>> > >> > >>>>>>> > >> > 1. these formats are not our core competency >>>>>>> > >> > 2. maintaining a complete set of these transformers >>>>>>> > >> across all the >>>>>>> > >> > popular formats du-jour is a large undertaking >>>>>>> > >> > 3. I am not convinced that >>>>>>> > >> > >>>>>>> > >> > All of these increase the technical risk. >>>>>>> > >> > >>>>>>> > >> > Additionally, to properly support this we'd really >>>>>>> need the >>>>>>> > >> ability to >>>>>>> > >> > then "map" multiple views for a given >>>>>>> entity-graph-root. >>>>>>> > >> What I mean by >>>>>>> > >> > that, is that such DTO approaches often need multiple >>>>>>> > >> "views" of a given >>>>>>> > >> > entity, e.g. a CompanyListDTO, CompanyOverviewDTO, >>>>>>> > >> > CompanyDetailsGeneralDTO, etc for a Company entity. >>>>>>> The >>>>>>> > >> point of this is >>>>>>> > >> > that >>>>>>> > >> > >>>>>>> > >> > 1. the transformers for these are specific to each >>>>>>> DTO >>>>>>> > >> type and would >>>>>>> > >> > be applied per-transformation >>>>>>> > >> > 2. were Hibernate to "provide" this for >>>>>>> applications >>>>>>> > >> > >>>>>>> > >> > IMO the use of queries to obtain views is logical. >>>>>>> > >> Populating each of >>>>>>> > >> > those specific DTOs (CompanyListDTO, etc) in the most >>>>>>> > >> efficient way is >>>>>>> > >> > going to require very different SQL for each DTO. >>>>>>> This >>>>>>> > >> implies some kind >>>>>>> > >> > of "mapping" to be able associate each DTO with query. >>>>>>> > >> > >>>>>>> > >> > Given 6.0's improved dynamic-instantiation support, I >>>>>>> even >>>>>>> > >> think that is a >>>>>>> > >> > great solution as well *for most cases*. >>>>>>> > >> > >>>>>>> > >> > So, while my objection has a "practical impact" >>>>>>> component, >>>>>>> > >> I also just >>>>>>> > >> > question whether Hibernate integrating with each >>>>>>> format's >>>>>>> > >> "serializer" is >>>>>>> > >> > the proper solution. >>>>>>> > >> > >>>>>>> > >> > >>>>>>> > >> > >>>>>>> > >> > On Thu, May 4, 2017 at 5:08 AM Christian Beikov < >>>>>>> > >> > christian.beikov(a)gmail.com >>>>>>> > >> <mailto:christian.beikov@gmail.com>> wrote: >>>>>>> > >> > >>>>>>> > >> >> This is exactly what I am trying to do with >>>>>>> > >> Blaze-Persistence Entity >>>>>>> > >> >> Views, making DTOs sexy and efficient :) >>>>>>> > >> >> >>>>>>> > >> >> Here a quick overview of how that looks like right >>>>>>> now: >>>>>>> > >> >> >>>>>>> > >> >> >>>>>>> > >> >>>>>>> > https://persistence.blazebit.com/documentation/entity-view/ >>>>>>> manual/en_US/index.html#first-entity-view-query >>>>>>> > >> < >>>>>>> > https://persistence.blazebit.com/documentation/entity-view/ >>>>>>> manual/en_US/index.html#first-entity-view-query >>>>>>> > > >>>>>>> > >> >> >>>>>>> > >> >> One of my targets is to make it possible to do >>>>>>> something >>>>>>> > >> like this >>>>>>> > >> >> >>>>>>> > >> >> entityManager.createQuery("FROM Order o", >>>>>>> > >> OrderDTO.class).getResultList() >>>>>>> > >> >> >>>>>>> > >> >> and get an optimal query, as well as objects with >>>>>>> only the >>>>>>> > >> necessary >>>>>>> > >> >> contents. >>>>>>> > >> >> >>>>>>> > >> >> Maybe we can collaborate on that somehow? >>>>>>> > >> >> >>>>>>> > >> >> >>>>>>> > >> >> Mit freundlichen Grüßen, >>>>>>> > >> >> >>>>>>> > >> >>>>>>> > ------------------------------------------------------------ >>>>>>> ------------ >>>>>>> > >> >> *Christian Beikov* >>>>>>> > >> >> Am 04.05.2017 um 10:20 schrieb Emmanuel Bernard: >>>>>>> > >> >> > Following up a bit on my previous email. >>>>>>> > >> >> > >>>>>>> > >> >> > While a core integration might be best I think, if >>>>>>> there >>>>>>> > >> are too much >>>>>>> > >> >> > reluctance, we can start with a dedicated >>>>>>> hibernate-dto >>>>>>> > >> or whatever >>>>>>> > >> >> > module or even separate project that makes life >>>>>>> easier >>>>>>> > >> for these "pass >>>>>>> > >> >> > through" use cases. This could be in the form of a >>>>>>> > >> wrapper API of sort >>>>>>> > >> >> > and hence not affect existing Hibernate ORM APIs. >>>>>>> > >> >> > >>>>>>> > >> >> > Note that the ResultTransformer approach feels >>>>>>> like it >>>>>>> > >> goes a long way >>>>>>> > >> >> > towards fixing the problem but as demonstrated in >>>>>>> Vlad's >>>>>>> > >> article >>>>>>> > >> >> > >>>>>>> > >> >> >>>>>>> > >> >>>>>>> > https://vladmihalcea.com/2017/04/03/why-you-should-use-the- >>>>>>> hibernate-resulttransformer-to-customize-result-set-mappings/ >>>>>>> > >> < >>>>>>> > https://vladmihalcea.com/2017/04/03/why-you-should-use-the- >>>>>>> hibernate-resulttransformer-to-customize-result-set-mappings/ >>>>>>> > > >>>>>>> > >> >> > it still requires quite a bit of code and a >>>>>>> special DTO >>>>>>> > >> constructor >>>>>>> > >> >> > object. That's what we need to get rid of I think. >>>>>>> > >> >> > >>>>>>> > >> >> > Emmanuel >>>>>>> > >> >> > >>>>>>> > >> >> > On Thu 17-05-04 10:04, Emmanuel Bernard wrote: >>>>>>> > >> >> >> I was very much in the Vlad, Steve, Christian camp >>>>>>> > >> until relatively >>>>>>> > >> >> >> recently. One of my main concern being that >>>>>>> replacing a >>>>>>> > >> proxy by null >>>>>>> > >> >> >> was really sending the wrong message. So I was >>>>>>> against >>>>>>> > >> having Hibernate >>>>>>> > >> >> >> ORM facilitate such a transformation. >>>>>>> > >> >> >> >>>>>>> > >> >> >> I am changing my mind because I am realizing that >>>>>>> a lot >>>>>>> > >> of applications >>>>>>> > >> >> >> are less complex that my perceived median. A lot >>>>>>> of >>>>>>> > >> apps really just >>>>>>> > >> >> >> want data to be fetched out and then passed to >>>>>>> jackson >>>>>>> > >> (implicitly) and >>>>>>> > >> >> >> pushed out as a REST response in JSON or some >>>>>>> other >>>>>>> > >> serialization >>>>>>> > >> >> >> protocol. >>>>>>> > >> >> >> >>>>>>> > >> >> >> So while we could try and keep the stance that >>>>>>> such a >>>>>>> > >> solution should >>>>>>> > >> >> >> remain out of scope of Hibernate ORM core, we >>>>>>> should >>>>>>> > >> have a very smooth >>>>>>> > >> >> >> integration with something like MapStruct to >>>>>>> create >>>>>>> > >> such bounded DTO on >>>>>>> > >> >> >> the fly. Ideally with as close to zero code as >>>>>>> possible >>>>>>> > >> from the user >>>>>>> > >> >> >> point of view. >>>>>>> > >> >> >> I can't really describe how that could look like >>>>>>> > >> because I am not >>>>>>> > >> >> >> familiar enough with MapStruct but I think it >>>>>>> should >>>>>>> > >> have the following >>>>>>> > >> >> >> characteristics: >>>>>>> > >> >> >> >>>>>>> > >> >> >> 1. do an implicit binding between the mapped >>>>>>> object >>>>>>> > >> graph and a >>>>>>> > >> >> detached >>>>>>> > >> >> >> object graph with a 1-1 mapping of type and >>>>>>> > >> replacing lazy objects >>>>>>> > >> >> and >>>>>>> > >> >> >> collections with null. That's the smoothest >>>>>>> approach >>>>>>> > >> and the most >>>>>>> > >> >> >> common use case but also the one where an >>>>>>> > >> inexperienced person could >>>>>>> > >> >> >> shoot at someone else's foot >>>>>>> > >> >> >> 2. do a binding between the mapped object graph >>>>>>> and a >>>>>>> > >> detached version >>>>>>> > >> >> of >>>>>>> > >> >> >> that object graph with a 1-1 mapping of type, >>>>>>> but >>>>>>> > >> declaratively >>>>>>> > >> >> >> expressing the boundaries for the detached >>>>>>> version. >>>>>>> > >> This enforces a >>>>>>> > >> >> >> clear thinking of the boundaries and will load >>>>>>> lazy >>>>>>> > >> data in case the >>>>>>> > >> >> >> object graph loaded is missing a bit. I like >>>>>>> the >>>>>>> > >> idea on principle >>>>>>> > >> >> but >>>>>>> > >> >> >> I think it overlaps a lot with the fetch graph. >>>>>>> > >> >> >> 3. offer a full integration between MapStruct and >>>>>>> > >> Hibernate ORM by >>>>>>> > >> >> >> letting people express a full fledge MapStruct >>>>>>> > >> transformation >>>>>>> > >> >> between >>>>>>> > >> >> >> the managed object graph and a different target >>>>>>> > >> structure >>>>>>> > >> >> >> >>>>>>> > >> >> >> I favored MapStruct over Dozer because we know the >>>>>>> > >> MapStruct lead >>>>>>> > >> >> quite well ;) >>>>>>> > >> >> >> >>>>>>> > >> >> >> Note however that the MapStruct approach requires >>>>>>> an >>>>>>> > >> explicit object >>>>>>> > >> >> >> copy, it feels a bit sad to have to double memory >>>>>>> > >> consumption. But that >>>>>>> > >> >> >> might be a good enough approach and bypassing the >>>>>>> > >> managed object >>>>>>> > >> >> >> creation leads to questions around the Persistence >>>>>>> > >> Context contract >>>>>>> > >> >> >> where loading an object supposedly means it will >>>>>>> be in >>>>>>> > >> the PC. >>>>>>> > >> >> >> Maybe a constructor like query syntax allowing to >>>>>>> > >> reference a MapStruct >>>>>>> > >> >> >> conversion logic might work? >>>>>>> > >> >> >> >>>>>>> > >> >> >> select mapStruct('order-and-items', o) from >>>>>>> Order o >>>>>>> > >> left join >>>>>>> > >> >> fetch o.items >>>>>>> > >> >> >> >>>>>>> > >> >> >> Emmanuel >>>>>>> > >> >> >> >>>>>>> > >> >> >> >>>>>>> > >> >> >> On Wed 17-04-19 14:29, Vlad Mihalcea wrote: >>>>>>> > >> >> >>> Hi, >>>>>>> > >> >> >>> >>>>>>> > >> >> >>> Although I keep on seeing this request from time >>>>>>> to >>>>>>> > >> time, I still >>>>>>> > >> >> think >>>>>>> > >> >> >>> it's more like a Code Smell. >>>>>>> > >> >> >>> Entities are useful for when you plan to modify >>>>>>> them. >>>>>>> > >> Otherwise, a DTO >>>>>>> > >> >> >>> projection is much more efficient, and you don't >>>>>>> > >> suffer from >>>>>>> > >> >> >>> LazyInitializationException. >>>>>>> > >> >> >>> >>>>>>> > >> >> >>> With the ResultTransformer, you can even build >>>>>>> graphs >>>>>>> > >> of entities, as >>>>>>> > >> >> >>> explained in this article; >>>>>>> > >> >> >>> >>>>>>> > >> >> >>> >>>>>>> > >> >> >>>>>>> > >> >>>>>>> > https://vladmihalcea.com/2017/04/03/why-you-should-use-the- >>>>>>> hibernate-resulttransformer-to-customize-result-set-mappings/ >>>>>>> > >> < >>>>>>> > https://vladmihalcea.com/2017/04/03/why-you-should-use-the- >>>>>>> hibernate-resulttransformer-to-customize-result-set-mappings/ >>>>>>> > > >>>>>>> > >> >> >>> >>>>>>> > >> >> >>> Due to how Hibernate Proxies are handled, without >>>>>>> > Bytecode >>>>>>> > >> >> Enhancement, >>>>>>> > >> >> >>> it's difficult to replace a Proxy with null >>>>>>> after the >>>>>>> > >> Session is >>>>>>> > >> >> closed. If >>>>>>> > >> >> >>> we implemented this, we'd have to take into >>>>>>> > >> consideration both >>>>>>> > >> >> Javassist >>>>>>> > >> >> >>> and ByteBuddy as well as ByteCode Enhancements. >>>>>>> > >> >> >>> >>>>>>> > >> >> >>> all in all, the implementation effort might not >>>>>>> > >> justify the benefit, >>>>>>> > >> >> and >>>>>>> > >> >> >>> I'm skeptical of offering a feature that does not >>>>>>> > >> encourage data >>>>>>> > >> >> access >>>>>>> > >> >> >>> Best Practices. >>>>>>> > >> >> >>> >>>>>>> > >> >> >>> Vlad >>>>>>> > >> >> >>> >>>>>>> > >> >> >>> On Wed, Apr 19, 2017 at 2:18 PM, Christian >>>>>>> Beikov < >>>>>>> > >> >> >>> christian.beikov(a)gmail.com >>>>>>> > >> <mailto:christian.beikov@gmail.com>> wrote: >>>>>>> > >> >> >>> >>>>>>> > >> >> >>>> Hey Romain, >>>>>>> > >> >> >>>> >>>>>>> > >> >> >>>> I don't think it is a good idea to expose >>>>>>> entities >>>>>>> > >> directly if you >>>>>>> > >> >> >>>> really need a subset of the data. >>>>>>> > >> >> >>>> Reasons for that thinking are that it gets hard >>>>>>> to >>>>>>> > >> define what needs >>>>>>> > >> >> to >>>>>>> > >> >> >>>> be fetched or is safe to be used for a >>>>>>> particular use >>>>>>> > >> case. Obviously >>>>>>> > >> >> >>>> serialization is like a follow-up problem. >>>>>>> > >> >> >>>> I see 2 possible solutions to the problem and >>>>>>> both >>>>>>> > >> boil down to the >>>>>>> > >> >> use >>>>>>> > >> >> >>>> of DTOs. >>>>>>> > >> >> >>>> >>>>>>> > >> >> >>>> 1. Use an object mapper(e.g. Dozer) that maps >>>>>>> > >> entity object graphs >>>>>>> > >> >> to >>>>>>> > >> >> >>>> custom DTO types. >>>>>>> > >> >> >>>> 2. Use specialized DTOs in queries. >>>>>>> > >> >> >>>> >>>>>>> > >> >> >>>> >>>>>>> > >> >> >>>> Implementing 1. does not help you with lazy >>>>>>> loading >>>>>>> > >> issues and 2. >>>>>>> > >> >> might >>>>>>> > >> >> >>>> require very intrusive changes in queries which >>>>>>> is >>>>>>> > >> why I implemented >>>>>>> > >> >> >>>> Blaze-Persistence Entity Views >>>>>>> > >> >> >>>> >>>>>>> > >> <https://github.com/beikov/ >>>>>>> blaze-persistence#entity-view-usage >>>>>>> > >> <https://github.com/beikov/ >>>>>>> blaze-persistence#entity-view-usage >>>>>>> > >>. >>>>>>> > >> >> >>>> This is a library that allows you to define >>>>>>> DTOs with >>>>>>> > >> mappings to the >>>>>>> > >> >> >>>> entity. In a query you can define that you want >>>>>>> > >> results to be >>>>>>> > >> >> >>>> "materialized" as instances of the DTO type. >>>>>>> > >> >> >>>> This reduces the pain induced by properly >>>>>>> separating the >>>>>>> > >> >> "presentation >>>>>>> > >> >> >>>> model" from the "persistence model" and at the >>>>>>> same >>>>>>> > >> time will improve >>>>>>> > >> >> >>>> the performance by utilizing the mapping >>>>>>> information. >>>>>>> > >> >> >>>> I don't want to advertise too much, just wanted >>>>>>> to >>>>>>> > >> say that I had the >>>>>>> > >> >> >>>> same issues over and over which is why I >>>>>>> started that >>>>>>> > >> project. >>>>>>> > >> >> >>>> >>>>>>> > >> >> >>>> Mit freundlichen Grüßen, >>>>>>> > >> >> >>>> >>>>>>> > >> >> >>>>>>> > >> >>>>>>> > ------------------------------------------------------------ >>>>>>> ------------ >>>>>>> > >> >> >>>> *Christian Beikov* >>>>>>> > >> >> >>>> Am 19.04.2017 um 10:51 schrieb Romain >>>>>>> Manni-Bucau: >>>>>>> > >> >> >>>>> Hi guys, >>>>>>> > >> >> >>>>> >>>>>>> > >> >> >>>>> Short sumarry: Wonder if hibernate could get a >>>>>>> > >> feature to kind of >>>>>>> > >> >> either >>>>>>> > >> >> >>>>> unproxy or freeze the entities once leaving the >>>>>>> > >> managed context to >>>>>>> > >> >> avoid >>>>>>> > >> >> >>>>> uncontrolled lazy loading on one side and >>>>>>> > >> serialization issues on >>>>>>> > >> >> another >>>>>>> > >> >> >>>>> side. >>>>>>> > >> >> >>>>> >>>>>>> > >> >> >>>>> Use case example: a common example is a REST >>>>>>> service >>>>>>> > >> exposing >>>>>>> > >> >> directly >>>>>>> > >> >> >>>>> hibernate entities (which is more and more >>>>>>> common >>>>>>> > >> with microservice >>>>>>> > >> >> >>>>> "movement"). >>>>>>> > >> >> >>>>> >>>>>>> > >> >> >>>>> Objective: the goal is to not need any step - >>>>>>> or >>>>>>> > >> reduce them a lot - >>>>>>> > >> >> >>>>> between the hibernate interaction and a >>>>>>> potential >>>>>>> > >> serialization to >>>>>>> > >> >> avoid >>>>>>> > >> >> >>>>> issues with lazy loading and unexpected >>>>>>> loading. >>>>>>> > >> Today it requires >>>>>>> > >> >> some >>>>>>> > >> >> >>>>> custom and hibernate specific logic in the >>>>>>> > >> serializer which kind of >>>>>>> > >> >> >>>> breaks >>>>>>> > >> >> >>>>> the transversality of the two concerns >>>>>>> > >> (serialization and object >>>>>>> > >> >> >>>>> management/loading). >>>>>>> > >> >> >>>>> >>>>>>> > >> >> >>>>> >>>>>>> > >> >> >>>>> Implementation options I see: >>>>>>> > >> >> >>>>> >>>>>>> > >> >> >>>>> 1. a callback requesting if the lazy >>>>>>> relationship >>>>>>> > >> should be fetched, >>>>>>> > >> >> >>>>> something like >>>>>>> > >> >> >>>>> >>>>>>> > >> >> >>>>> public interface GraphVisitor { >>>>>>> > >> >> >>>>> boolean shouldLoad(Object rootEntity, >>>>>>> Property >>>>>>> > >> property); >>>>>>> > >> >> >>>>> } >>>>>>> > >> >> >>>>> >>>>>>> > >> >> >>>>> 2. An utility to remove any proxy potentially >>>>>>> > >> throwing an exception >>>>>>> > >> >> and >>>>>>> > >> >> >>>>> replacing the value by null or an empty >>>>>>> collection, >>>>>>> > >> something like >>>>>>> > >> >> >>>>> >>>>>>> > >> >> >>>>> MyEntity e = Hibernate.deepUnproxy(entity); >>>>>>> > >> >> >>>>> >>>>>>> > >> >> >>>>> 3. A switch of the proxy implementation, this >>>>>>> is >>>>>>> > >> close to 2 but >>>>>>> > >> >> wouldn't >>>>>>> > >> >> >>>>> require a call to any utility, just a >>>>>>> configuration >>>>>>> > >> in the >>>>>>> > >> >> persistence >>>>>>> > >> >> >>>> unit. >>>>>>> > >> >> >>>>> Side note: of course all 3 options can be >>>>>>> mixed to >>>>>>> > >> create a single >>>>>>> > >> >> >>>> solution >>>>>>> > >> >> >>>>> like having 3 implemented based on 1 for >>>>>>> instance. >>>>>>> > >> >> >>>>> >>>>>>> > >> >> >>>>> Configuration proposal: this would be activated >>>>>>> > >> through a property >>>>>>> > >> >> in the >>>>>>> > >> >> >>>>> persistence unit (this shouldn't be only >>>>>>> global IMHO >>>>>>> > >> cause >>>>>>> > >> >> otherwise you >>>>>>> > >> >> >>>>> can't mix 2 kind of units, like one for JSF >>>>>>> and one >>>>>>> > >> for JAX-RS to be >>>>>>> > >> >> >>>>> concrete). This should also be activable as a >>>>>>> query >>>>>>> > >> hint i think - >>>>>>> > >> >> but >>>>>>> > >> >> >>>> more >>>>>>> > >> >> >>>>> a nice to have. >>>>>>> > >> >> >>>>> >>>>>>> > >> >> >>>>> >>>>>>> > >> >> >>>>> What this feature wouldn't be responsible for: >>>>>>> > >> cycles. If >>>>>>> > >> >> relationships >>>>>>> > >> >> >>>> are >>>>>>> > >> >> >>>>> bidirectional then the unproxied entity would >>>>>>> still >>>>>>> > >> "loop" if you >>>>>>> > >> >> browse >>>>>>> > >> >> >>>>> the object graph - this responsability would >>>>>>> stay in >>>>>>> > >> the consumer >>>>>>> > >> >> since >>>>>>> > >> >> >>>> it >>>>>>> > >> >> >>>>> doesn't depend on hibernate directly but more >>>>>>> on a >>>>>>> > >> plain object >>>>>>> > >> >> handling. >>>>>>> > >> >> >>>>> >>>>>>> > >> >> >>>>> What do you think? >>>>>>> > >> >> >>>>> >>>>>>> > >> >> >>>>> >>>>>>> > >> >> >>>>> Romain Manni-Bucau >>>>>>> > >> >> >>>>> @rmannibucau <https://twitter.com/ rmannibucau >>>>>>> > >> <https://twitter.com/rmannibucau>> | Blog >>>>>>> > >> >> >>>>> <https://blog-rmannibucau.rhcloud.com >>>>>>> > >> <https://blog-rmannibucau.rhcloud.com>> | Old Blog >>>>>>> > >> >> >>>>> <http://rmannibucau.wordpress.com >>>>>>> > >> <http://rmannibucau.wordpress.com>> | Github < >>>>>>> > https://github.com/ >>>>>>> > >> >> >>>> rmannibucau> | >>>>>>> > >> >> >>>>> LinkedIn <https://www.linkedin.com/in/ >>>>>>> rmannibucau >>>>>>> > >> <https://www.linkedin.com/in/rmannibucau>> | JavaEE >>>>>>> Factory >>>>>>> > >> >> >>>>> <https://javaeefactory- rmannibucau.rhcloud.com >>>>>>> > >> <https://javaeefactory-rmannibucau.rhcloud.com>> >>>>>>> > >> >> >>>>> ______________________________ >>>>>>> _________________ >>>>>>> > >> >> >>>>> hibernate-dev mailing list >>>>>>> > >> >> >>>>> hibernate-dev(a)lists.jboss.org >>>>>>> > >> <mailto:hibernate-dev@lists.jboss.org> >>>>>>> > >> >> >>>>> >>>>>>> > >> https://lists.jboss.org/ mailman/listinfo/hibernate-dev >>>>>>> > >> <https://lists.jboss.org/ mailman/listinfo/hibernate-dev >>>>>>> > >>>>>>> > >> >> >>>> ______________________________ _________________ >>>>>>> > >> >> >>>> hibernate-dev mailing list >>>>>>> > >> >> >>>> hibernate-dev(a)lists.jboss.org >>>>>>> > >> <mailto:hibernate-dev@lists.jboss.org> >>>>>>> > >> >> >>>> >>>>>>> > >> https://lists.jboss.org/ mailman/listinfo/hibernate-dev >>>>>>> > >> <https://lists.jboss.org/ mailman/listinfo/hibernate-dev >>>>>>> > >>>>>>> > >> >> >>>> >>>>>>> > >> >> >>> ______________________________ _________________ >>>>>>> > >> >> >>> hibernate-dev mailing list >>>>>>> > >> >> >>> hibernate-dev(a)lists.jboss.org >>>>>>> > >> <mailto:hibernate-dev@lists.jboss.org> >>>>>>> > >> >> >>> https://lists.jboss.org/ >>>>>>> mailman/listinfo/hibernate-dev >>>>>>> > >> <https://lists.jboss.org/ mailman/listinfo/hibernate-dev >>>>>>> > >>>>>>> > >> >> >> _______________________________________________ >>>>>>> > >> >> >> hibernate-dev mailing list >>>>>>> > >> >> >> hibernate-dev(a)lists.jboss.org >>>>>>> > >> <mailto:hibernate-dev@lists.jboss.org> >>>>>>> > >> >> >> https://lists.jboss.org/ >>>>>>> mailman/listinfo/hibernate-dev >>>>>>> > >> <https://lists.jboss.org/ mailman/listinfo/hibernate-dev >>>>>>> > >>>>>>> > >> >> > _______________________________________________ >>>>>>> > >> >> > hibernate-dev mailing list >>>>>>> > >> >> > hibernate-dev(a)lists.jboss.org >>>>>>> > >> <mailto:hibernate-dev@lists.jboss.org> >>>>>>> > >> >> > https://lists.jboss.org/ >>>>>>> mailman/listinfo/hibernate-dev >>>>>>> > >> <https://lists.jboss.org/ mailman/listinfo/hibernate-dev >>>>>>> > >>>>>>> > >> >> >>>>>>> > >> >> _______________________________________________ >>>>>>> > >> >> hibernate-dev mailing list >>>>>>> > >> >> hibernate-dev(a)lists.jboss.org >>>>>>> > >> <mailto:hibernate-dev@lists.jboss.org> >>>>>>> > >> >> https://lists.jboss.org/ >>>>>>> mailman/listinfo/hibernate-dev >>>>>>> > >> <https://lists.jboss.org/ mailman/listinfo/hibernate-dev >>>>>>> > >>>>>>> > >> >> >>>>>>> > >> > >>>>>>> > >> _______________________________________________ >>>>>>> > >> hibernate-dev mailing list >>>>>>> > >> hibernate-dev(a)lists.jboss.org >>>>>>> > >> <mailto:hibernate-dev@lists.jboss.org> >>>>>>> > >> https://lists.jboss.org/ mailman/listinfo/hibernate-dev >>>>>>> > >> <https://lists.jboss.org/ mailman/listinfo/hibernate-dev >>>>>>> > >>>>>>> > >> >>>>>>> > > >>>>>>> > > >>>>>>> > >>>>>>> > _______________________________________________ >>>>>>> > hibernate-dev mailing list >>>>>>> > hibernate-dev(a)lists.jboss.org >>>>>>> > https://lists.jboss.org/mailman/listinfo/hibernate-dev >>>>>>> _______________________________________________ >>>>>>> hibernate-dev mailing list >>>>>>> hibernate-dev(a)lists.jboss.org >>>>>>> https://lists.jboss.org/mailman/listinfo/hibernate-dev >>>>>>> >>>>>> >>>>>> >>>>>> _______________________________________________ hibernate-dev mailing list hibernate-dev(a)lists.jboss.org https://lists.jboss.org/mailman/listinfo/hibernate-dev