Hi,
I don't think I understand exactly what I'm supposed to pass to the
foreign_keys parameter to relation.
I'm trying to set up a 1-to-many viewonly relation, with no backref,
where there are two intermediate tables between the parent table and the
child. To complicate things further, I need to restrict the rows by
joining against a couple of other tables as well.
I was previously running on a fairly old version of SA (revision 2283),
and the relation seemed to work correctly when I ANDed all of my
conditions together and passed them to relation as the primaryjoin.
However, I just tried 0.3.6 and got "ArgumentError: Cant locate any
foreign key columns ... Specify foreign_keys argument ..."
(Interestingly, if I try 0.3.5, the relation compiles but when I try to
access it I get a different exception, InvalidRequestError, about a
column not being available because it conflicts with another one)
For example, if these are my tables:
#------------------------------------------------------------------
# Three entities, 'a', 'b' and 'c'.
# 'a' and 'b' have a many-to-many relationship
# 'b' and 'c' have a many-to-many relationship
a_table = Table('a', metadata,
Column('id', Integer, primary_key=True),
Column('name', String(16)),
)
b_table = Table('b', metadata,
Column('id', Integer, primary_key=True),
Column('name', String(16)),
)
c_table = Table('c', metadata,
Column('id', Integer, primary_key=True),
Column('name', String(16)),
)
a_b_table = Table('a_b', metadata,
Column('a_id', Integer, ForeignKey('a.id'),
primary_key=True),
Column('b_id', Integer, ForeignKey('b.id'),
primary_key=True),
)
b_c_table = Table('b_c', metadata,
Column('b_id', Integer, ForeignKey('b.id'),
primary_key=True),
Column('c_id', Integer, ForeignKey('c.id'),
primary_key=True)
)
class A(object):
pass
class B(object):
pass
class C(object):
pass
mapper(B, b_table)
mapper(C, c_table)
#############################################################
# How can I create a mapper on A with a property that gives
# all the 'C' objects?
#############################################################
# This doesn't work - it requires the foreign_keys parameter
# to be passed, but I don't know what to pass.
mapper(
A, a_table,
properties={'cs': relation(primaryjoin=and_(a_table.c.id ==
a_b_table.c.a_id,
a_b_table.c.b_id ==
b_c_table.c.b_id,
c_table.c.id ==
b_c_table.c.c_id),
viewonly=True,
)
}
)
#------------------------------------------------------------------
I probably haven't explained myself very well. I've tried lots of ways
of expressing the relation, including passing a select as an association
table, but I can't seem to get it to work. Does anyone have any ideas?
Thanks a lot,
Simon
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