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From "Reece Garrett (JIRA)" <>
Subject [jira] Commented: (OPENJPA-235) SQL reordering to avoid non-nullable foreign key constraint violations
Date Wed, 13 Jun 2007 16:57:25 GMT


Reece Garrett commented on OPENJPA-235:

Hello all,

I would like to know if anyone has plans or is in the process of implementing Markus's solution?
 Obviously, based on the interest this has generated, it is an important addition to OpenJPA.
However, for the moment I can not devote anymore development hours to working on a new patch.
Right now we are dealing with unique keys by...not using them. This will work in the short
term but we'll have to find a way to handle them soon. Perhaps at that point I'll get more
hours to work on a patch but  I'm a bit apprehensive because as I mentioned earlier, it will
require going a bit deeper in to the code to store original values to calculate unique key
dependencies. It is also difficult working on this without access to the TCK tests.

As Markus suggests, the solution is basically the current implementation in ConstraintUpdateManager
with provisions for capturing dereferenced rows to calculate update-delete dependencies (my
second patch does this), circular reference handling (my second patch does minimal handling
but Markus's solution is better), deadlock prevention, and of course unique key dependencies.


> 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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