>
> In case of RelatedJoins SQLObject deletes objects from the
intermediate
> table itself because the table can be hidden from the user at all - it is
> usually automatically created and maintained.
>
Ok, I just realized that my example was bad. This one's better:
class Top(sqlobject.SQLObject):
a = sqlobject.SQLMultipleJoin('A')
class AB(sqlobject.SQLObject):
a = sqlobject.ForeignKey('A', cascade = True)
b = sqlobject.ForeignKey('B', cascade = True)
class A(sqlobject.SQLObject):
top = sqlobject.ForeignKey('Top', cascade = True)
b = sqlobject.RelatedJoin('B', intermediateTable = AB.sqlmeta.table,
createRelatedTable = False)
class B(sqlobject.SQLObject):
a = sqlobject.RelatedJoin('A', intermediateTable = AB.sqlmeta.table,
createRelatedTable = False)
Top.createTable(ifNotExists = True)
A.createTable(ifNotExists = True)
B.createTable(ifNotExists = True)
AB.createTable(ifNotExists = True)
[a.destroySelf() for a in A.select()]
[b.destroySelf() for b in B.select()]
[ab.destroySelf() for ab in AB.select()]
top = Top()
a1 = A(top = top)
a2 = A(top = top)
a3 = A(top = top)
a4 = A(top = top)
b1 = B()
b2 = B()
b3 = B()
b4 = B()
a1.addB(b1)
a1.addB(b2)
a2.addB(b1)
a2.addB(b2)
a2.addB(b3)
a3.addB(b4)
a4.addB(b2)
a4.addB(b4)
# Slow:
top.destroySelf()
# Fast:
# Top.deleteBy(id = top.id)
The first destroy statement results in these queries:
1/Select : SELECT a.id, a.top_id FROM a WHERE ((a.top_id) = (5))
2/Query : DELETE FROM ab WHERE a_id=17
1/Select : SELECT ab.id, ab.a_id, ab.b_id FROM ab WHERE ((ab.a_id) =
(17))
2/Query : DELETE FROM ab WHERE a_id=17
1/Query : DELETE FROM a WHERE id = (17)
2/Query : DELETE FROM ab WHERE a_id=18
1/Select : SELECT ab.id, ab.a_id, ab.b_id FROM ab WHERE ((ab.a_id) =
(18))
2/Query : DELETE FROM ab WHERE a_id=18
1/Query : DELETE FROM a WHERE id = (18)
2/Query : DELETE FROM ab WHERE a_id=19
1/Select : SELECT ab.id, ab.a_id, ab.b_id FROM ab WHERE ((ab.a_id) =
(19))
2/Query : DELETE FROM ab WHERE a_id=19
1/Query : DELETE FROM a WHERE id = (19)
2/Query : DELETE FROM ab WHERE a_id=20
1/Select : SELECT ab.id, ab.a_id, ab.b_id FROM ab WHERE ((ab.a_id) =
(20))
2/Query : DELETE FROM ab WHERE a_id=20
1/Query : DELETE FROM a WHERE id = (20)
2/Query : DELETE FROM top WHERE id = (5)
1/Query : DELETE FROM top WHERE id = 5
whereas the second destroy statement produces just
1/Query : DELETE FROM top WHERE id = 4
It seems like sqlobject is iterating though all of top's siblings in order
to destroy them. In case I have many of these siblings, the DB is able to
perform this operations magnitudes faster than sqlobject. Is deleteBy() the
preferred (the only?) way for doing just this?
Thanks,
Bernhard
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