Re: [hibernate-dev] [feature request][discuss] smoother serializers integration?
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>
|
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