On Feb 27, 2014, at 9:23 PM, Seth P <spadow...@gmail.com> wrote: > Thank you. This was very helpful. > > One non-trivial thing that stumped me for a while is that if B is derived > from a B_base using joined-table inheritance, and the order variable is in > the base table B_base, then it seems one must include B_base explicitly -- as > highlighted below.
OK well maybe you just include B_base in the primaryjoin and not “B” at all? you want to include as few tables as possible in these things to keep the query plans simpler. > > from sqlalchemy import Column, Integer, ForeignKey, create_engine, select, > join > from sqlalchemy.orm import create_session, relationship, backref, mapper > from sqlalchemy.ext.declarative import declarative_base > from sqlalchemy.ext.associationproxy import association_proxy > > sqlite = 'sqlite:///test_a_to_b.db' > e = create_engine(sqlite, echo=True) > Base = declarative_base(bind=e) > > class A(Base): > __tablename__ = 'a' > id = Column(Integer, primary_key=True) > bs = association_proxy("a_to_bs", "b", creator=lambda x: A_to_B(b=x)) > > class B_base(Base): > __tablename__ = 'b_base' > id = Column(Integer, primary_key=True) > order = Column(Integer) > > class B(B_base): > __tablename__ = 'b' > id = Column(Integer, ForeignKey(str(B_base.__table__) + ".id"), > primary_key=True) > > class A_to_B(Base): > __tablename__ = 'a_to_b' > id = Column(Integer, primary_key=True) > a_id = Column(Integer, ForeignKey(str(A.__table__) + ".id"), > nullable=False, index=True) > a = relationship(A, foreign_keys=[a_id], > backref=backref("a_to_bs", primaryjoin="and_(A_to_B.a_id > == A.id, A_to_B.b_id == B.id, B.id == B_base.id)", order_by="B.order")) > b_id = Column(Integer, ForeignKey(str(B.__table__) + ".id"), > nullable=False) > b = relationship(B, foreign_keys=[b_id], lazy="subquery") > def __init__(self, a=None, b=None): > self.a = a > self.b = b > > if __name__ == '__main__': > # recreate database > Base.metadata.drop_all() > Base.metadata.create_all() > # populate > session = create_session(bind=e, autocommit=False) > a = A(bs=[B(order=10), B(order=2)]) > session.add(a) > session.commit() > session.close_all() > # read > session = create_session(bind=e, autocommit=False) > a = session.query(A).one() > for b in a.bs: > print b.order > for a_to_b in a.a_to_bs: > print a_to_b.b.order > session.close_all() > > > -- > You received this message because you are subscribed to the Google Groups > "sqlalchemy" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to sqlalchemy+unsubscr...@googlegroups.com. > To post to this group, send email to sqlalchemy@googlegroups.com. > Visit this group at http://groups.google.com/group/sqlalchemy. > For more options, visit https://groups.google.com/groups/opt_out.
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