Thank you again Michael!
It is really awesome, I can just add to the resources collection and it
will "know" what is the correct reverse action.
Em sábado, 13 de julho de 2013 16h06min55s UTC-3, Alexandre Torres escreveu:
>
> Oh, it was so easy!
>
> XMapper = mapper(X, C_table, properties={
> 'resources': relationship(A,collection_class=set,*back_populates='action'*
> )})
>
> AMapper = mapper(A,pjoin,with_polymorphic=('*',
> pjoin),polymorphic_on=pjoin.c.type,properties={
> 'action' : relationship(X) # no back_populates, it will never happens
> anyway
> })
>
>
> L1Mapper = mapper(L1,L1_table,inherits=AMapper,
> concrete=True,
> polymorphic_identity='l1',properties={
> 'action' : relationship(X,primaryjoin=(X_table.c.id==L1_table.c.id_idx),*
> back_populates='resources'* )
>
> Now I understand... no need for back-ref
>
> Em sábado, 13 de julho de 2013 10h13min50s UTC-3, Alexandre Torres
> escreveu:
>>
>> Hi again,
>>
>> I implemented a relationship using back_populates using the example
>>
>> http://docs.sqlalchemy.org/en/latest/orm/inheritance.html#relationships-with-concrete-inheritance
>>
>> But I stumbled in a problem: My super class A does not have a table, it
>> is based in a polymorphic union (thanks Michael for the great tip in my
>> last post).
>>
>> X<->A
>> A <-- L1
>> A<--L2 ...
>>
>> XMapper = mapper(X, C_table, properties={
>> 'resources': relationship(A,collection_class=set,*back_populates='action'
>> *)})
>>
>> AMapper = mapper(A,pjoin,with_polymorphic=('*',
>> pjoin),polymorphic_on=pjoin.c.type)
>>
>> L1Mapper = mapper(L1,L1_table,inherits=AMapper,
>> concrete=True,
>> polymorphic_identity='l1',properties={
>> 'action' :
>> relationship(X,primaryjoin=(X_table.c.id==L1_table.c.id_idx),back_populates='resources'
>>
>> )
>> #... (L2 is pretty much the same)
>>
>> This produces an error because my A mapper does not implement the *resources
>> *relationship:
>> "sqlalchemy.exc.InvalidRequestError: Mapper 'Mapper|A|pjoin' has no
>> property 'action'"
>> But If I remove the first *back_populates='action'*, it works. Well, for
>> a read only collection...
>> My question is this: is there a way to make SQLAlchemy understand that
>> class A is abstract and therefore does not implements the relationship?
>> Or is there another option , such as declaring action as a property? I
>> tried that, but without much success.
>>
>> By the way, in my experience (what I can recall), no other ORM tool
>> automatically allows this kind of complex bidirectional behaviour with
>> concrete inheritance ;)
>> that would be awesome.
>>
>>
>>
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