SQLAlchemy targets mapped entities in a result set by their position
within the Query object's entities. It's not possible to have a UNION
that returns some objects of type A and then some objects of type B in
the same position, unless those two classes are related through
polymorphic inheritance with a discriminator.
On Mon Jun 16 10:36:04 2014, Craig Sabbey wrote:
> I'm trying to union the same query for 2 tables with the same
> structure, along with joinedloads for these tables. When I use
> DBSession([TABLE]) for each query in the union, the columns come back
> in different orders. If I specify the columns
> (DBSession([TABLE.COL_A], [TABLE.COL_B], ...) then the joinedloads
> fail with "Query has only expression-based entities".
>
> Here is some pseudo-code to hopefully make it clear what I'm trying to do:
>
> q0 = DBSession.query(T0).options(joinedload('ref')
> q1 = DBSession.query(T1).options(joinedload('ref')
> return q0.union_all(q1).all()
>
> Is there another way to perform this query?
>
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