thats definitely not going to work right now. I added feature
enhancement # 740, currently its milestone 5 unless we start getting
more time for some of these things. put primary_key on your Table
for now.
On Aug 15, 2007, at 12:04 PM, Alberto Valverde wrote:
> from sqlalchemy import *
>
> meta = MetaData()
> engine = create_engine('sqlite:///:memory:', echo=True)
> meta.bind = engine
>
> # Tables
> rel1 = Table('rel1', meta,
> Column('id', Integer, primary_key=True),
> Column('data', Unicode),
> )
>
> rel2 = Table('rel2', meta,
> Column('id', Integer, primary_key=True),
> Column('data', Unicode),
> )
>
>
> hub = Table('hub', meta,
> Column('time', DateTime, nullable=False),
> Column('rel1_id', Integer, ForeignKey('rel1.id'), nullable=False),
> Column('rel2_id', Integer, ForeignKey('rel2.id'), nullable=False),
>
> # Mapped schema doesn't use a primary key since it's a "hub" table
> # in a fact system and "time" doesn't have enough resolution to
> guarantee
> # uniqueness.
> #XXX Uncommenting the following line fixes it.
> ##PrimaryKeyConstraint('time', 'rel1_id', 'rel2_id'),
>
> Column('data', Unicode),
> )
>
> # Mapped classes
> class Hub(object): pass
> class Rel1(object): pass
> class Rel2(object): pass
>
> # mappers
> mapper(Rel1, rel1)
> mapper(Rel2, rel2)
> mapper(Hub, hub,
> # A PK must be "faked" in the mapper to be able to map it (some
> rows are
> # missed due to duped pk when retrieving with the mapper but
> it's not much
> # of a problem since the schema is mostly queried without the
> ORM for data
> # analysisi).
> primary_key = [hub.c.time, hub.c.rel1_id, hub.c.rel2_id],
> properties = dict(
> #XXX: Making the relations lazy fixes it too.
> rel1 = relation(Rel1, lazy=False),
> rel2 = relation(Rel2, lazy=False),
> )
> )
>
> def run_test():
> meta.create_all()
> sess = create_session(bind_to=engine)
> # No limit, no problem
> sess.query(Hub).select()
> # Bang!
> sess.query(Hub).select(limit=100)
>
> if __name__ == '__main__':
> run_test()
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