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https://issues.apache.org/jira/browse/OPENJPA-235?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Fay Wang updated OPENJPA-235:
-----------------------------
Attachment: openjpa.patch
I did some investigation about the OptimisticLock exception where
ConstraintUpdateManager is used when entity A is deleted:
@Entity A {
@OneToMany(cascade=CascadeType.ALL, mappedBy="a")
List b;
}
@Entity B {
@ForeignKey(deleteAction=ForeignKeyAction.CASCADE)
@ManyToOne(cascade=CascadeType.MERGE)
A a;
}
It is found that if the foreign key delete action is set to "on delete
restrict", the deletion of A is fine without OptimisticLock exception. It turns
out that
ConstraintUpdateManager only re-order the deletions of entities for foreign
key on delete restrict such that the child rows (entity B) are deleted first
before the parent rows (entity A) are deleted. This re-ordering should also be
applied to foreign key on delete cascade.
With foreign key on delete cascade, if the parent row is deleted first, the
child rows will be deleted automatically by the database, resulting in
OptimiticLock exception (b/c the child rows (entity B) are no longer there
when openjpa tries to delete them.)
The attached patch adds support for foreign key on delete cascade so that the
ConstraintUpdateManager will re-order the deletions of entities to prevent
OptimiticLock exception.
> 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: 1.2.0
>
> Attachments: merge-detached.patch, merge-testcases.patch,
> openjpa-235-break-nullable-070716.patch, openjpa-235-break-nullable.patch,
> openjpa-235-test.jar, openjpa-235-test1.jar, openjpa-235-test2.zip,
> openjpa.patch, openjpa.patch, 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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