On May 5, 2010, at 5:01 PM, Timmy Chan wrote:
> i have 4 tables, a, b, c, d.
>
> a has one-to-many relation with b, b with one-to-one relationship with c, c
> is a polymorphic on a.type, with d being one of the polymorphic types.
>
> is there a way to implement this?
>
> details:
>
> this is what im trying to do in sqlalchemy:
>
> a = Table('a', metadata,
> Column( 'id', Integer(), primary_key=True ),
> Column( 'type', UnicodeText() ) )
>
> b = Table('b', metadata,
> Column( 'id', Integer(), primary_key=True ),
> Column( 'a_id', Integer(), ForeignKey('a.id') ) )
>
> c = Table('c', metadata,
> Column( 'id', Integer(), primary_key=True ),
> Column( 'b_id', Integer(), ForeignKey('b.id') ),
> Column( 'class_id', Integer() ) )
>
> d = Table('d', metadata,
> Column( 'id', Integer(), primary_key=True ),
> Column( 'data', Integer() )
>
> mappers
>
> mapper( A, a )
> mapper( B, b, properties={'a': relationship( A, uselist=False,backref='b',
> 'c':relationship( C, uselist=False, backref='b') })
>
> # Does a full join, does not work
> mapper( C, c, polymorphic_on = a.c.type )
> mapper( D, d, inherits=C, polymorphic_identity = "D" )
>
>
> how can i change c to polymorphic on a, through the relationship? is there
> a way to sort by d.data? (b-c/d is one-on-one).
this mapping is incorrect. mapper(C) cannot be polymorphic on a table which
is not part of its mapping, and mapper(C) does not contain an "inherits"
keyword to that of A. Usually the "polymorphic_on" setting is on the
base-most mapper in the hierarchy and its not clear here which mapper you
intend for that to be.
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