Filter by compound fields in SQLAlchemy - sqlalchemy

Question

How can I filter by multiple fields using SQLAlchemy's ORM?
Example:
SELECT p.* FROM product p
WHERE (p.barcode, p.partner) NOT IN (
SELECT barcode, partner
FROM unallowed_products
);

Answer 1

Lets define some aliases in order to reduce verbosity before looking at possible solutions:
P, U = Product, UnallowedProduct
version-1: OUTER JOIN + WHERE IS NULL
This is quite universal solution and should work with all backends (RDBMS)
q = (
session.query(P)
.outerjoin(U, and_(P.barcode == U.barcode, P.partner == U.partner))
.filter(U.id == None)
)
version-2: tuple comparison
This does not work for all backends, but should work for mySQL, postgresql
See tuple_ documentation
q = (
session.query(P)
.filter(~tuple_(P.barcode, P.partner).in_(
select([U.barcode, U.partner])
))
)
version-3: use multiple OR statements
See this answer.
There is no reason to use it as version-1 and version-2 are cleaner.
version-4: concatenation of barcode and partner into one column
See this question.
This is basically your own solution.
Again, there is not reason to use it as other versions are much cleaner, and do not require conversions to strings etc.

Answer 2

This query should solve the problem:
SELECT p.* FROM product p
WHERE (p.barcode || "_" || p.partner) NOT IN (
SELECT barcode || "_" || partner
FROM unallowed_products
);
which can be translated to SQLAlchemy ORM like this:
subquery = session.query(
cast(UnallowedProducts.barcode, type_=Text) +
'_' +
cast(UnallowedProducts.partner, type_=Text)
).subquery()
session.query(Product)\
.filter((
cast(Product.id, type_=Text) +
'_' +
cast(Product.partner, type_=Text)
).notin_(subquery))
This tricky solution should work for virtually every case.