odd passive_deletes setting raises

from sqlalchemy import *
from sqlalchemy.orm import *
from sqlalchemy.ext.declarative import declarative_base

Base = declarative_base(create_engine('postgres://scott:tiger@127.0.0.1/test', echo=True))

class Parent(Base):
    __tablename__ = 'parent'

    id  = Column(Integer, primary_key=True)
    data = Column(String)
    child_id = Column(Integer, ForeignKey('child.id'))
    child = relation("Child", cascade="all, delete", passive_deletes=True)

class Child(Base):
    __tablename__ = 'child'

    id  = Column(Integer, primary_key=True)
    data = Column(String)


Base.metadata.drop_all()
Base.metadata.create_all()

s = create_session()

p1 = Parent(data='p1', child=Child(data='c1'))
s.add(p1)
s.flush()

s.clear()

p1 = s.query(Parent).get(p1.id)
s.delete(p1)
s.flush()

the question here is, do we disable the above setting, raise a warning, or actually try to support it, since while ON DELETE CASCADE doesn't work for M2O, a trigger can be used to achieve this effect.

we might try adding a test which simulates a trigger with a ME, or uses a real trigger.

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