[hibernate-dev] Wrapping up 5.4.0

[Steve Ebersole]

JPA's EntityGraph feature is cumbersome to define and use.  Hibernate 5.4
adds 2 new features to help make working with EntityGraphs easier.

*EntityGraph parsing*

The first feature is the ability to create a graph from a String
representation.  E.g., given a Person entity, we might want to make sure
the Person's spouse is eagerly fetched:
````
    final EntityGraph eg = org.hibernate.graph.EntityGraphs.parse(
Person.class, "spouse", entityManager );
    final Person personAndSpouse = entityManager.find( Person.class, 1,
Collections.singletonMap( "javax.persistence.fetchgraph", eg );
````

This parsing supports all of the features of EntityGraph creation including
sub-graphs (though see second feature) and sub-class graphs.  See the
documentation for in-depth discussion and examples.

*EntityGraph manipulation*

This is mainly about combining graphs.  E.g.

````
    final EntityGraph eg1 = org.hibernate.graph.EntityGraphs.parse(
Person.class, "spouse", entityManager );
    final EntityGraph eg2 = org.hibernate.graph.EntityGraphs.parse(
Person.class, "spouse(age, dob)", entityManager );
    final EntityGraph combinedGraph
= org.hibernate.graph.EntityGraphs#merge( entityManager, Person.class, eg1,
eg2 )
    final Person personAndSpouse = entityManager.find( Person.class, 1,
Collections.singletonMap( "javax.persistence.fetchgraph", combinedGraph );
````

This is a very trivial example meant just for illustration.  It can
actually be much more easily defined as:

````
    final EntityGraph combinedGraph =
org.hibernate.graph.EntityGraphs.parse( Person.class, "spouse( age, dob )",
entityManager );
    final Person personAndSpouse = entityManager.find( Person.class, 1,
Collections.singletonMap( "javax.persistence.fetchgraph", combinedGraph );
````


P.S. Looking back at this, I wonder if we want to combine
`org.hibernate.graph.GraphParser` into `org.hibernate.graph.EntityGraphs`.
As-is, users wanting to use both of these features above would need to
import both of those classes.  What do y'all think?


On Mon, Nov 5, 2018 at 5:41 PM Steve Ebersole <steve at hibernate.org> wrote:

> With regard to entity graphs, the only new piece is the "parse a string
> representation" feature.  I'll write up a release notes blurb with a simple
> code sample, but the new documentation sections cover this feature very
> in-depth.
>
>
>
> On Mon, Nov 5, 2018 at 12:07 PM Guillaume Smet <guillaume.smet at gmail.com>
> wrote:
>
>> Hi,
>>
>> If everybody is OK with it, I would like to wrap 5.4.0.CR1 on Wednesday
>> 14th (this is next Wednesday).
>>
>> That means that everything we want in 5.4.0 should be in by then.
>>
>> The big remaining subject IMHO is this one:
>> https://github.com/hibernate/hibernate-orm/pull/2611 . I think we really
>> need that in.
>>
>> Chris, Gail, do you think you can drive this puppy home before then?
>>
>> If you have issues affected to you that you know won't be fixed before
>> next
>> Wednesday, can you please move them to 5.4.1 so that we have a clear
>> vision
>> of the remaining work?
>>
>> Steve, could you please prepare a paragraph about the entity graph work
>> for
>> the announcement? As it's the big new feature of this release, some code
>> showing the improvements made would be welcome, I think.
>>
>> Thanks!
>>
>> --
>> Guillaume
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>