In JBoss 3.0.x, <cascade-delete> deletes child entities one at a time.
This makes sense when an in-memory cache needs to be maintained -- you
need to know which entities to remove from the cache.
But when there is no cache (e.g., commit option C), there are several
more efficient approaches:
a. delete all children in a single step
DELETE FROM Child WHERE ParentId = <parent-key>
DELETE FROM Parent WHERE Id = <parent-key>
(Others have suggested this one as well)
b. leverage the database's own ON DELETE CASCADE
CREATE TABLE Child
...
ParentId FOREIGN KEY REFERENCES Parent(Id) ON DELETE CASCADE
DELETE FROM Parent WHERE Id = <parent-key>
One nice property of (b), for the databases which support it and for
applications without caching, is that the CMP code needs to do very
little! :-) ON DELETE CASCADE is supported by at least Oracle and
SqlServer.
BTW, I would not expect the <create-table> element to create this
FOREIGN KEY (that is a bit much, given the slightly different SQL
syntaxes involved), but it would be ideal if there were a configuration
option to tell CMP that such a DB constraint existed.
I have searched jboss-user, jboss-development, the forums, and the task
list, and I am not sure whether this is a planned feature or not. It
sounds like there are tons of CMP improvements in the works for 4.0 --
is a configuration option to use the database's ON DELETE CASCADE one of
them?
Thanks,
-- Randy
_________________________________________________________________
Randy Shoup
Tumbleweed Communications Corporation
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