Question

I have searched many topics and didn’t find the answer, or question was too complex. So okay. This is my first question.
Here is the SQL

SELECT  parent.*,
(
    SELECT  COUNT(*)
    FROM    child
    WHERE   parent.id = child.parent_id
)
FROM parent

How to do this clause in sqlalchemy?

WHERE   ui.invited_by = u.id

Can it be reproduced in collections ? sql expressions ?
P.S. I know that it can be done by group_by. But i need by subquery.

Thank you.

Answer 1

I find here really awesome answer. But too also too complicated. First of all i want to tell that closure in sql world is CORRELATION.

This is NOT the same but helps me.

pparent = Parent.__table__.alias('pparent') # using table directly to alias.

subquery = s.query(count(Child.id)).join(pparent) # usual thing but use aliased table.

s.query(Parent, subquery.filter(Parent.id == pparent.id).correlate(Parent).as_scalar()) #magic