That seems easy enough, thanks!
On Jul 28, 7:25 pm, Michael Bayer <[email protected]> wrote:
> On Jul 28, 2009, at 8:14 PM, NoDamage wrote:
>
>
>
>
>
> > Is it possible to manually set the type column of a base class when
> > using single table inheritance? The reason I want to do this is
> > because I am importing data from an external source which does not
> > differentiate between the subclass types.
>
> > For example:
>
> > a_table = Table('a', metadata,
> > Column('id', Integer, primary_key=True),
> > Column('type', String(20)),
> > Column('name', String(20))
> > )
>
> > class A(object): pass
> > class B(A): pass
>
> > a_mapper = mapper(A, a_table, polymorphic_on=a_table.c.type,
> > polymorphic_identity='a', with_polymorphic='*')
> > b_mapper = mapper(B, inherits=a_mapper, polymorphic_identity='b')
>
> > Here, A is the base class and B is the subclass. I want to be able to
> > do this:
>
> > a = A()
> > a.type = 'b'
>
> > session.add(a)
> > result = session.query(A).all()
>
> > I expect the result to contain an instance of B because I have
> > explicitly set the type to 'b'. But right now, it looks like because I
> > have instantiated an instance of A, the type is overwritten as 'a'. Is
> > there any nice way to do this?
>
> you could just say:
>
> a.__class__ = B
>
> seems a little weird but it is probably the most "pythonic" way to go.
>
> at the moment the flush() process overwrites the "type" column
> regardless of what's in it. Theres no hard reason it has to be that
> way, but im hesitant to change it right now within 0.5 since its been
> that way for a long time and could break people's applications.
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