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From "Markus Fuchs (JIRA)" <j...@apache.org>
Subject [jira] Updated: (OPENJPA-235) SQL reordering to avoid non-nullable foreign key constraint violations
Date Sat, 26 May 2007 00:55:16 GMT

     [ https://issues.apache.org/jira/browse/OPENJPA-235?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Markus Fuchs updated OPENJPA-235:
---------------------------------

    Attachment: openjpa-235-test1.jar

Hi Reece,

Thanks for trying my test case. I've been playing around with commit dependencies, and this
is, what I found:

1) One reason, why your previous patch didn't work is, as you already found out, that the
rows returned by RowManagerImpl.getInserts returns are not in user order. This might be unexpected
and should either be documented or changed (I haven't found any usages of RowManagerImpl.getInserts
in the current code, so it might be possible to change that). An alternative would be to add
a new method RowManagerImpl.getOrderedInserts.

2) Another situation, that generally doesn't work (both w/ your patch and w/o), is when relationships
are nullified before the objects are deleted. Please see my new test openjpa-235-test1. OpenJPA
doesn't execute updates for deleted objects. There will be a fk constraint violation if the
updates are skipped and the objects aren't modified according to the constraint dependencies
inside the user transaction. I couldn't find how to get "old" relationship value before the
update, which would be needed for the dependency calculation.

3) It seems, that join table entries are removed from the non-owning side. IMHO, relationship
updates should only be done from the owning side.

> 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
>         Assigned To: Patrick Linskey
>             Fix For: 0.9.8
>
>         Attachments: openjpa-235-test.jar, openjpa-235-test1.jar, sqlreorder.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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