On Tue, May 22, 2018 at 3:48 PM, Demitri Muna <demitri.m...@gmail.com> wrote:
> Hi Mike,
>
> Thanks for the quick reply. I added the "concrete=True" to the B class
> definition and got this error:
>
>> AttributeError: Concrete Mapper|B|b does not implement attribute 'type' at
>> the instance level. Add this property explicitly to Mapper|B|b.
>
>
> Although is a subclass of A (as defined above), the "type" relationship
> appears lost. OK, I'll add it back to the B definition:
>
> type_pk = Column("type_pk", Integer, ForeignKey(Type.pk))
>
> type = relationship(Type, primaryjoin=Type.pk==type_pk)
>
> I used the same label for "backref" initially and got a "property of that
> name exists" error. I them omitted the backref as above.
>
> This works exactly as I'd hoped! I create a B object, it's inserted into the
> database as expected (visible in the A and B tables). When I perform a query
> to retrieve all A objects, the correct number is returned and some of them
> are correctly typed B. The defined relationships work. I tried creating a
> "backref" with a unique name, and that worked, but I found that wasn't
> necessary if I'm happy using the same name. When going from the type mapped
> to A, I get a list of A objects (excluding B); when going from the type of
> B, I get the list of just the B objects.
>
> Is there a way to set the type_pk discriminator in the B class as a default
> so I don't have to set it every time?
I should probably get a complete version of your codes so I can try it
sometime, I would think that since this discriminator column is
already set, it should be getting populated (maybe redefine it in the
__mapper_args__ for "b" to this local copy of the column).
if none of that works then I'd hit it with a default or event, if it's
local to "b" then just place "default=<discrimiminator>" on the
column. or if you need more control of the process use a
before_insert event.
>
> Thanks!
>
> Demitri
>
>
>
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