On Jun 6, 2011, at 7:13 PM, Geoff wrote:
> On Jun 6, 11:32 pm, Michael Bayer <[email protected]> wrote:
>>
>> The table referenced by "secondary=" in a relationship() is managed
>> entirely, regardless of cascade setting, but
>> only from the perspective of the parent. Meaning if A references a
>> collection of B, the row in a_to_b will be
>> deleted if you 1. delete A, or 2. remove a B from A's collection. Deleting
>> a B by itself as in session.delete(B)
>> won't have an effect unless you apply a backref to the relationship so that
>> each B also knows about its collection
>> of A.
>
> I am indeed deleting B but in this case I do have the backref
> specified in the parent table A e.g.
>
> Class A(Base):
> toB = relationship('B', secondary=a_b, backref='toA')
Below is a short test, can you figure out what you might be doing differently ?
from sqlalchemy import create_engine, Column, Integer, Table, ForeignKey
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.orm import Session, relationship
Base = declarative_base()
class A(Base):
__tablename__ = 'a'
id = Column(Integer, primary_key=True)
related = relationship("B",
secondary=Table(
'secondary',
Base.metadata,
Column('aid', Integer, ForeignKey('a.id'),
primary_key=True),
Column('bid', Integer, ForeignKey('b.id'),
primary_key=True)),
backref="related_a"
)
class B(Base):
__tablename__ = 'b'
id = Column(Integer, primary_key=True)
engine = create_engine("sqlite://", echo=True)
Base.metadata.create_all(engine)
s = Session(engine)
b1, b2, b3 = B(), B(), B()
a1 = A(related=[b1, b2, b3])
s.add(a1)
s.commit()
assert s.query(Base.metadata.tables['secondary']).count() == 3
s.delete(b2)
s.commit()
assert s.query(Base.metadata.tables['secondary']).count() == 2
>
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