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https://issues.apache.org/jira/browse/OPENJPA-235?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12506964
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Reece Garrett commented on OPENJPA-235:
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Kevan,
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 ordering.
-Reece
> 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, openjpa-235-test2.zip, 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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