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From Bryan Lewis <br...@maine.rr.com>
Subject how to catch updates just before commit
Date Fri, 28 Apr 2006 16:40:25 GMT
We have a time-when-last-modified timestamp column in most of our tables
to serve as an optimistic-locking attribute.  At present we're setting
it with a bit of inelegant code that imitates the way we used to do it
in our old WebObjects days... we have a saveChanges() method that wraps
dc.commitChanges().  Before the commit we can timesstamp the newObjects
and modifiedObjects.

The trouble is, this sets the timestamp on objects that haven't really
been modified... an attribute was set to the same value it already had,
or a to-many relationship was added to.  Cayenne figures out later in
the pipeline that those other changes aren't real and doesn't generate
SQL for them.  How can I hook into that later point, and set the
timestamp only if the row is about to be updated?  I looked at
DataContextDelegate, but I guess that's for external changes.  The event
mechanism looks closer, although the docs say that dc.onSync() isn't
intended for direct use.  Worst case, I could compare the object's
current values to the snapshot but that seems reinventing the plumbing.

Thanks.


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