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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