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https://issues.apache.org/jira/browse/OPENJPA-235?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12500481
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Gokhan Ergul commented on OPENJPA-235:
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Reece --thanks for trying them out, good news indeed on the attached-merge
front. The issue with detached testcase is as follows: merge A cascades to B,
which in turn cascades to C, since the relations between A -> B and B -> C are
annotated with Cascade.ALL on OneToMany sides. But as there's no cascade
annotation on ManyToOne side (owner side of bidirectional relation), when
AttachManager tries to attach those fields (such as C.parent), it encounters a
new object (an instance of EntityB), and complains as such. In all fairness,
that's correct -- B is a new object and there's no Cascade.MERGE from C.parent
to B. The missing piece of information is, that B object has already been
attached (evidently since manager._attached map contains it) as part of that
"merge session" so to speak --that's the object via which AttachManager got to
object C in the first place, and B will be persisted as part of the same
transaction. So there's no grounds to reject it. That's what the patch I
attached along with the testcase does. If you could go ahead and apply it, you
should no longer see that error.
> SQL reordering to avoid non-nullable foreign key constraint violations
> ----------------------------------------------------------------------
>
> Key: OPENJPA-235
> URL: https://issues.apache.org/jira/browse/OPENJPA-235
> Project: OpenJPA
> Issue Type: Improvement
> Components: kernel
> Reporter: Reece Garrett
> Assignee: Patrick Linskey
> Fix For: 0.9.8
>
> Attachments: merge-detached.patch,
> merge-multigen-collection-testcase.zip, openjpa-235-test.jar,
> openjpa-235-test1.jar, sqlreorder.patch, sqlReorder2.patch
>
>
> OpenJPA does not do any SQL statement re-ordering in order to resolve foreign
> key constraints. Instead, objects are always inserted in the order in which
> the user persists the instances. When you persist in an order that would
> violate foreign key constraints, OpenJPA attempts to insert null and then
> update the foreign key value in a separate statement. If you use non-nullable
> constraints, though, you must persist your objects in the correct order.
> This improvement re-orders SQL statements as follows:
> 1. First, all insert statements execute. Inserts which have foreign keys with
> non-nullable constraints execute AFTER the foreign keys which they depend on
> have been inserted since no deferred update is possible.
> 2. Next, all update statements execute. No reordering is necessary.
> 3. Finally, all delete statements execute. Like inserts, deletes execute in
> an order which does not violate non-nullable foreign key constraints.
> If a circular foreign key reference is found during the re-ordering process
> then re-ordering halts and the remaining unordered statements are left as is.
> There is nothing that can be done about the circular reference (other than
> fixing the schema) and the resulting SQL statements will not succeed.
> The net effect is that users do not need to worry about the persistence order
> of their objects regardless of non-nullable foreign key constraints. The only
> class modified was
> org.apache.openjpa.jdbc.kernel.OperationOrderUpdateManager. I have included a
> patch which includes my modifications to OperationOrderUpdateManager and test
> cases. The test cases I have provided fail on the current trunk but pass with
> my modifications. I have also verified that I did not break anything by using
> maven to run all test cases with my modifications in place.
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