Michael Bayer ha scritto:
the original mapping essentially expressed this relationship:
A <-- cascade="all, delete-orphan" --> B
in both directions. What that means is, there cannot be an A with no B
in the database, and there cannot be a B with no A in the database,
i.e. its either A<->B or both will be deleted. its like an oxygen
molecule, or something.
what you need to do is decide which of A and B can exist on its own
without a parent relationship. since you want to delete rows from B
and not A, that would indicate that the mapping should be:
mapper(A, a)
mapper(
B, b,
properties={
'a': relation(
A, backref=backref('b', lazy=False, uselist=False,
cascade='all, delete-orphan'),
uselist=False
)
}
)
i.e. the "delete-orphan" cascade is only in the direction from A->B.
the cascade from B->A is left at its default value of "save-update", so
delete operations dont propigate from B's to A's.
Thanks, this works.
The problem was with my original exemple where I create a session
without binding it to a connection.
Regards Manlio Perillo
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