Thank you for the clarifications.
On 10/18/2012 11:43 AM, Michael Bayer wrote:
On Oct 17, 2012, at 9:55 PM, Kent wrote:
The attached script fails with "sqlalchemy.exc.InvalidRequestError: Instance '<Bug at
0x1e6f3d10>' has been deleted. Use the make_transient() function to send this object back
to the transient state."
While this example is somewhat convoluted, I have a few questions about
sqlalchemy behavior here:
1) At the session.flush(), even though the Rock and the bugs relationship have
been expunged, the pending delete still is issued to the database. Would you
expect/intend sqlalchemy to delete even after the expunge()?
no, because the Rock you have merged has established that the Bug is no longer
associated with it. You expunge the Rock, there's no Bug attached to it to be
expunged.
2) After the flush(), shouldn't the history of the 'bugs' relationship have
been updated to reflect the statement issued to the database? (See print
statement)
yes, because merged is not in that Session anymore. The flush() is what
resets the history. Clearly it's not going to go out to find objects that
aren't in that Session.
3) The InvalidRequestError is only raised if the 'bugs' relationship has a
backref, otherwise it isn't raised. Any idea why?
removing the Bug.rock path means that when you expunge "merged", there is
nothing left in the flush process to handle the orphan cascade you're looking for here.
The DELETE does not occur so the Bug that's present on merged can go right back in.
4) Don't hate me for asking: is there a work around? I'm trying to understand
this scenario since in a rare case, it presents.
The workaround is don't use expunge(). This is not a method I ever use for
anything, actually. And especially, if you manipulate the state within the
Session, then expunge() random segments of that state, you can hardly expect
flush() to have a clear idea of what you intend.
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