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From "Gokhan Ergul (JIRA)" <>
Subject [jira] Commented: (OPENJPA-235) SQL reordering to avoid non-nullable foreign key constraint violations
Date Thu, 31 May 2007 20:39:15 GMT


Gokhan Ergul commented on OPENJPA-235:

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:
>             Project: OpenJPA
>          Issue Type: Improvement
>          Components: kernel
>            Reporter: Reece Garrett
>            Assignee: Patrick Linskey
>             Fix For: 0.9.8
>         Attachments: merge-detached.patch,, 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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