How would you use proxies? I can get B.a_re.children.b_re, but this
includes all Bs that have different B.id than I want along with the ones I
do want. I could just use a @property that issues SQL on every call, but
I'm trying to see if there are more efficient ways of doing this.
On Tuesday, June 11, 2013 4:18:20 PM UTC-5, Michael Bayer wrote:
>
>
> getting it to work with "secondary" or only "primaryjoin" as it sometimes
> works out is fairly complex and might not be possible. If "secondary",
> you might need to make "secondary" an aliased SELECT statement, or in 0.9
> maybe it can be a a JOIN, that represents all the intermediary rows. Might
> work, might not, would have to spend a few hours with it.
>
> Is there a reason you can't just route to the related B.a.children.bsusing
> proxies? Or a @property based loader?
>
>
>
>
> On Jun 11, 2013, at 4:45 PM, Greg Yang <sorcer...@gmail.com <javascript:>>
> wrote:
>
> Consider these 2 mapped classes
>
> from sqlalchemy.engine import create_engine
> from sqlalchemy.ext.associationproxy import association_proxy
> from sqlalchemy.ext.declarative.api import declarative_base
> from sqlalchemy.orm import relationship
> from sqlalchemy.orm.session import sessionmaker
> from sqlalchemy.orm.util import aliased
> from sqlalchemy.schema import Column, ForeignKey
> from sqlalchemy.sql.expression import and_
> from sqlalchemy.types import Integer, String
>
> Base = declarative_base()
>
> class A(Base):
> __tablename__ = 'table_a'
> id = Column(Integer, primary_key=True)
> child_id = Column(Integer, ForeignKey('table_a.id'))
> children = relationship('A', backref = 'parent', remote_side=[id])
> class B(Base):
> __tablename__ = 'table_b'
> id = Column(Integer, primary_key=True)
> a_id = Column(Integer, ForeignKey('table_a.id'), primary_key=True)
> a_re = relationship('A', backref='b_re')
>
> What I want to do is have a self-referential relationship in B that routes
> through A's children relationship while keeping B.id the same. More
> explicitly I want some relationship B.children such that for any instance
> beta of B
>
> for b in beta.children:
> assert b.id == beta.id
> assert b.a_re in beta.a_re.children
>
> Now, if the condition b.id == beta.id is ignored, then it's just a plain
> association table many-to-many relationship, something like
>
> B.children = relationship('B', secondary=A.__table__,
> primaryjoin=B.a_id==A.id, secondaryjoin=B.a_id==A.child_id, viewonly=True)
>
> But with the b.id == beta.id condition I need to refer to table_b twice
> in the join table_b JOIN table_a JOIN table_b, and I'm not sure how to do
> that in relationship.
>
> I've tried this
>
> BB = aliased(B)
> B.children = relationship('BB', secondary=A.__table__,
> primaryjoin=B.a_id==A.id,
> secondaryjoin='''and_(A.id==BB.a_id,
> B.id==BB.id)''',
> viewonly=True)
>
> but it seems like BB is not recognized by the ORM in mapping.
>
> How do I do this?
>
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