I have the schema described in the test script located
here: http://pastebin.com/qeB0vKVV
If you run the script, you can see that there is a
ConcurrentModificationError: when I go to delete the contest. If I delete
the contestants first, there is no problem. The problem seems to be caused
by the double link between "Contest" and "Contestant". The first, an
indirect link via TeamContestant through polymorphic inheritance created by
the m1 mapper, and the second a backref created by the m2 mapper. If I
leave the Contest.team_contestant relation off, the script executes
successfully. Removing that relation changes the order of the operations:
when it works successfully, all Slot updates happen before the first delete
operation. When it fails, the contestants are deleted before the slots are
updated as follows:
Echo output of a successful run:
2010-12-18 21:37:56,788 INFO sqlalchemy.engine.base.Engine.0x...2890 UPDATE
slot SET contest_id=? WHERE slot.id = ?
2010-12-18 21:37:56,788 INFO sqlalchemy.engine.base.Engine.0x...2890 (None,
1)
2010-12-18 21:37:56,788 INFO sqlalchemy.engine.base.Engine.0x...2890 UPDATE
slot SET contestant_id=? WHERE slot.id = ?
2010-12-18 21:37:56,788 INFO sqlalchemy.engine.base.Engine.0x...2890 (None,
2)
2010-12-18 21:37:56,789 INFO sqlalchemy.engine.base.Engine.0x...2890 UPDATE
slot SET contestant_id=? WHERE slot.id = ?
2010-12-18 21:37:56,789 INFO sqlalchemy.engine.base.Engine.0x...2890 (None,
3)
2010-12-18 21:37:56,789 INFO sqlalchemy.engine.base.Engine.0x...2890 DELETE
FROM team_contestant WHERE team_contestant.id = ?
2010-12-18 21:37:56,789 INFO sqlalchemy.engine.base.Engine.0x...2890 ((1,),
(2,))
2010-12-18 21:37:56,790 INFO sqlalchemy.engine.base.Engine.0x...2890 DELETE
FROM contestant WHERE contestant.id = ?
2010-12-18 21:37:56,790 INFO sqlalchemy.engine.base.Engine.0x...2890 ((1,),
(2,))
2010-12-18 21:37:56,790 INFO sqlalchemy.engine.base.Engine.0x...2890 DELETE
FROM contest WHERE contest.id = ?
2010-12-18 21:37:56,790 INFO sqlalchemy.engine.base.Engine.0x...2890 (1,)
Echo from an unsuccessful run:
2010-12-18 17:25:59,017 INFO sqlalchemy.engine.base.Engine.0x...2490 DELETE
FROM contestants WHERE contestants.contest_id = %(contest_id)s
2010-12-18 17:25:59,017 INFO sqlalchemy.engine.base.Engine.0x...2490
({'contest_id': 267}, {'contest_id': 267})
2010-12-18 17:25:59,025 INFO sqlalchemy.engine.base.Engine.0x...2490 UPDATE
slots SET contest_id=%(contest_id)s WHERE slots.id = %(slot_id)s
2010-12-18 17:25:59,025 INFO sqlalchemy.engine.base.Engine.0x...2490
{'contest_id': None, 'slot_id': 4}
2010-12-18 17:25:59,026 INFO sqlalchemy.engine.base.Engine.0x...2490 UPDATE
slots SET contestant_id=%(contestant_id)s WHERE slots.id = %(slot_id)s
2010-12-18 17:25:59,027 INFO sqlalchemy.engine.base.Engine.0x...2490
{'contestant_id': None, 'slot_id': 8}
2010-12-18 17:25:59,027 INFO sqlalchemy.engine.base.Engine.0x...2490 UPDATE
slots SET contestant_id=%(contestant_id)s WHERE slots.slot_id = %(slot_id)s
2010-12-18 17:25:59,027 INFO sqlalchemy.engine.base.Engine.0x...2490
{'contestant_id': None, 'slot_id': 9}
I would expect the Contest.team_contestants relation, since it contains no
explicit cascade, to not take precedence over the more inclusive
Contest.contestants. It looks like however that the rowcount calculation
takes one relation, while the delete takes the other. Is there a bug there?
I can actually use viewonly on the team_contestants relation. This seems to
cause the correct behavior to occur. Luckily I'm not writing to the
team_contestant relation, so I don't think this will adversely affect my
application.
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