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https://issues.apache.org/jira/browse/OPENJPA-782?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12681095#action_12681095
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Fay Wang commented on OPENJPA-782:
----------------------------------
Spec 2.5 Embeddable Classes (p 34):
"Since instances of embeddable classes themselves have no persistent identity,
the relationship from the referenced entity is to the entity that contains the
embeddable instance(s) and not to the embeddable itself."
Spec 10.1.26 ManyToOne Annotation (p. 310):
"The ManyToOne annotation may be used within an embeddable class to specify a
relationship from the embeddable class to an entity class."
Spec 10.1.35 OneToOne Annotation (p.323):
"The OneToOne annotation may be used within an embeddable class to specify a
relationship from the embeddable class to an entity class. "
Case (1):
EntityA
======
private Collection<EmbedA> embedAs;
EmbedA:
========
@ManyToOne
EntityB entityB;
The values for EntityA, EmbedA, EntityB can be:
EntityA1 - EmbedA1 - EntityB1
EmbedA2 - EntityB1
EmbedA3 - EntityB2
EmbedA4 - EntityB2
The implied relation from EntityA to EntityB is therefore OneToMany. A
bi-directional relation between EntityA and EntityB (spec p.40) suggests that
the relation from EntityB to EntityA is ManyToOne.
EntityB:
=======
@ManyToOne
private EntityA entityA;
Case(2):
EntityA
======
private Collection<EmbedA> embedAs;
EmbedA:
========
@OneToOne
EntityB entityB;
The values for EntityA, EmbedA, EntityB can be:
EntityA1 - EmbedA1 - EntityB1
EmbedA2 - EntityB2
EmbedA3 - EntityB3
EmbedA4 - EntityB4
The implied relation from EntityA to EntityB is therefore OneToMany. A
bi-directional relation between EntityA and EntityB (spec p.40) suggests that
the relation from EntityB to EntityA is ManyToOne.
EntityB:
=======
@ManyToOne
private EntityA entityA;
In both cases, EntityA should be the owning side (as it contains EmbedA). In
order to specify bi-directional relation, the mappedBy annotation should be
specified in EntityB, However, EntityB has ManyToOne relation, which disallows
"mappedBy" to be specified. Therefore, IMO, it is not possible to specify
bi-directional relation when a collection embeddables is involved.
> Support for collections of embeddables and basic types
> ------------------------------------------------------
>
> Key: OPENJPA-782
> URL: https://issues.apache.org/jira/browse/OPENJPA-782
> Project: OpenJPA
> Issue Type: Sub-task
> Reporter: Fay Wang
> Assignee: Fay Wang
> Fix For: 2.0.0
>
> Attachments: openjpa-782-testcase.patch, openjpa-782.patch
>
>
> Regarding jpa 2.0 embeddable, suppose Entity A contains a collection of
> embeddables.
> The collection of embeddable is stored in a separate table. @CollectionTable
> can be used to specify the table name, etc. If the @CollectionTable is not
> used, a default table name is used (see spec, p 272 ).
> The embeddable may contain the relation to EntityB in the following scenarios:
> (1) If in the embeddable, there is:
> @ManyToOne
> private EnittyB entityB;
>
> then the relation from EntityA to EntityB is OneToMany,
> and the relation from EntityB to EntityA is ManyToOne (Spec 2.5):
> @ManyToOne
> private EntityA entityA;
> (2) If in the embeddable, there is:
> @OneToOne
> private EntityB;
> then the relation from EntityA to EntityB is OneToMany,
> and the relation from EntityB to EntityA is ManyToOne (Spec 2.5):
> @ManyToOne
> private EntityA entityA;
> (3) If in the embeddable, there is:
> @OneToOne(mappedBy = "entityB")
> private EntityB
> The relation from EntityA to EnityB is OneToMany,
> and the relation from EntityB to EntityA is ManyToOne:
> @ManyToOne
> private EntityA entityA;
> The relation to EntityB will be stored in the third table (the
> CollectionTable) so that it can be associated with the embeddable. However,
> we can not use "mappedBy" in the ManyToOne relation in EntityB. How to have
> bi-directional relation between EntityA and EntityB in these situations? Is
> it possible to have a bi-directional relation between these two entities when
> embeddable is involved as described above?
> In scenario (3), an explicit "mappedBy" is specified in the embeddable, so
> that the bi-directional relation between EntityA and EntityB will be stored
> in the EntityB table, but then how can we associate EntityB with the
> embeddable when EntityA is retrieved back as embeddable itself does not have
> identity?
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