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From "Reece Garrett (JIRA)" <>
Subject [jira] Commented: (OPENJPA-235) SQL reordering to avoid non-nullable foreign key constraint violations
Date Thu, 21 Jun 2007 17:26:26 GMT


Reece Garrett commented on OPENJPA-235:


Concerning the exceptions you're getting, one of my colleagues suggested (and I agree) that
 OpenJPA may not know about some foreign keys due to missing foreign key annotations. There
are several cases where OpenJPA defines logical foreign keys but not actual foreign keys unless
explicitly instructed to do so by the @ForeignKey or @ElementForeignKey annotations. I was
not able to detect logical foreign keys when calculating dependencies between rows. I solved
this problem by explicitly declaring the foreign keys I was missiong. Logical foreign keys
worked well before the patch because the code did not need to detect the foreign keys for


> 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, sqlReorderTests.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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