Ah, so, it turns out to be more subtle than I first thought. It took me
quite a while to narrow it down to an easily reproducible case. To trigger
the behavior you need to be: joinedloading() along a backref, and also I
think it matters that I am joining back onto the same table and returning a
bunch of objects. Quite a corner case I think.
This code demonstrates the behavior - it issues a second query in the for
loop for the 'A' which has no child.
from sqlalchemy import *
from sqlalchemy.orm import *
from sqlalchemy.ext.declarative import declarative_base
Base = declarative_base()
class A(Base):
__tablename__ = 'a'
id = Column(Integer, primary_key=True)
join_table = Table('parent_child', Base.metadata,
Column('id_a', ForeignKey('a.id')),
Column('id_b', ForeignKey('a.id')))
parent = relationship("A",
secondary=join_table,
primaryjoin = (id == join_table.c.id_a),
secondaryjoin = (id == join_table.c.id_b),
uselist=False,
backref=backref("child", uselist=False))
e = create_engine("sqlite://", echo=True)
Base.metadata.create_all(e)
sess = Session(e)
a1 = A()
a2 = A(parent=a1)
sess.add(a1)
sess.add(a2)
sess.commit()
sess.close()
results = sess.query(A).options(joinedload("child")).all()
print "----"
for a in results:
print a.child is None
On Mon, Mar 24, 2014 at 8:34 PM, Michael Bayer <mike...@zzzcomputing.com>wrote:
>
> On Mar 24, 2014, at 2:09 PM, Philip Scott <safetyfirstp...@gmail.com>
> wrote:
>
> >
> > Is this a bug, or perhaps some expected side effect of the joined load?
>
> seemed like something that might be possible but the scalar loader is
> initializing the attribute to None to start with, here's a simple test that
> doesn't show your behavior, so see if you can just modify this one to show
> what you are seeing. note we only need to see that 'bs' is in a1.__dict__
> to prevent a lazyload.
>
> from sqlalchemy import *
> from sqlalchemy.orm import *
> from sqlalchemy.ext.declarative import declarative_base
>
> Base = declarative_base()
>
> class A(Base):
> __tablename__ = 'a'
>
> id = Column(Integer, primary_key=True)
> bs = relationship("B", secondary=Table('atob', Base.metadata,
> Column('aid', ForeignKey('a.id')),
> Column('bid', ForeignKey('b.id'))
> ),
> uselist=False)
>
> class B(Base):
> __tablename__ = 'b'
>
> id = Column(Integer, primary_key=True)
>
> e = create_engine("sqlite://", echo=True)
> Base.metadata.create_all(e)
>
> sess = Session(e)
> sess.add(A())
> sess.commit()
> sess.close()
>
> a1 = sess.query(A).options(joinedload("bs")).first()
> assert 'bs' in a1.__dict__
> assert a1.__dict__['bs'] is None
> assert a1.bs is None
>
>
>
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