the join() function, given two tables, will make a foreign key join
condition by default if you dont specify the "onclause". but if you
arent using a "join" function somewhere, then nothing else is going
to generate any clauses for you.
On Feb 27, 2007, at 10:50 AM, Rick Morrison wrote:
> Shouldn't SA be able to figure out the following joins without
> needing the explicit join params?
>
> I've got to be missing something dumb.
>
> from sqlalchemy import *
>
> metadata = BoundMetaData('sqlite:///:memory:')
>
> ent = Table('entity', metadata,
> Column('id', INT, Sequence('entity_id'),
> primary_key=True, nullable=False),
> Column('nm', VARCHAR(12), nullable=False)
> )
>
> loc = Table('location', metadata,
> Column('id', INT, Sequence('location_id'),
> primary_key=True, nullable=False),
> Column('nm', VARCHAR(50))
> )
>
> el = Table('el_rel', metadata,
> Column('typ', VARCHAR(12), nullable=False),
> Column('ident', INT, ForeignKey(' entity.id'),
> nullable=False),
> Column('idloc', INT, ForeignKey('location.id'),
> nullable=False)
> )
>
> metadata.create_all()
>
> ent.insert ().execute({'id':1, 'nm':'Eone'}, {'id':2,
> 'nm':'Etwo'}, {'id':3, 'nm':'Ethree'})
> loc.insert().execute({'id':1, 'nm':'Lone'}, {'id':2, 'nm':'Ltwo'},
> {'id':3, 'nm':'Lthree'})
> el.insert().execute({'typ':'TEST1', 'ident':1, 'idloc':1},
> {'typ':'TEST2', 'ident':2, 'idloc':2})
>
> testcases = [('2-way ->ent', [ent.c.nm ], None),
> ('2-way ->loc', [loc.c.nm], None),
> ('3-way ->ent+loc', [ent.c.nm, loc.c.nm], None),
> ('3-way, explicit join', [ent.c.nm, loc.c.nm],
> el.join(ent, ent.c.id==el.c.ident).join(loc,
> loc.c.id==el.c.idloc))
> ]
>
> for test_name, test_cols, test_from in testcases:
> print
> print test_name
> q = select(test_cols, el.c.typ == 'TEST1')
> if test_from:
> q.append_from(test_from)
> print str(q)
> print q.execute().fetchall()
>
>
>
> Thx,
> Rick
>
> >
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