what query do you want to see when you select "C" and "D" objects ?
On May 5, 2010, at 5:26 PM, Timmy Chan wrote:
> thx, is there a way to set that up, or something similar?
>
> after giving it thought, maybe polymorphic_on isn't what i need. in some
> sense, table "A" is similar to a generic container, and i want to constrain
> the type of "C" depending on "A"'s type column. is there a way to do this?
>
> On Wed, May 5, 2010 at 5:15 PM, Michael Bayer <mike...@zzzcomputing.com>
> wrote:
>
> 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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