I would advise against using from_statement(). the Query object supports
cte() and subqueries directly, see the example at
https://docs.sqlalchemy.org/en/13/orm/query.html?highlight=query%20cte#sqlalchemy.orm.query.Query.cte
alternatively if you are using 1.4 beta1 then you can use session.execute()
directly using a select() object.
On Tue, Nov 10, 2020, at 2:37 AM, kris wrote:
>
> I need to query over a table mapped to class T,
> I usually use session.query (T), however I am using two cte's
>
> part0 = ... cte('part0')
> part1 = ... cte('part1')
> part2 = ...
> cte('aprt2')
> allparts = union
> (part1.select(), part2.select())
>
> session.query (allparts) .. returns row record but I need it to return
> objects of type T?
>
> I have tried using q1 = session.query(T).from_statement (allnodes)
> which appears to convert and create objects of T, However,
> I cannot filter or order_by
>
> I have tried using the sql epxression level:
> n = allparts.alias()
> DBSession.query (T).from_statement (select ([n]).where (...).order_by
> (...)).all()
> or
> DBSession.query(T).from_statement(DBSession.query
> (n).filter(...).order_by(...).statement).
>
> but I get NoSuchColumnError: "Could not locate column in row for column
> 'T.id'"
>
> Is there a way to let SA know how map the columns of the select expression to
> an object?
>
> Thanks.
>
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