Querying from list of related in SQLalchemy and Flask

Question

I have User which has-one Person. So User.person is a Person.
I am trying to get a list of User from a list of Person.

I tried the following:

>>> people = Person.query.filter().limit(3)
<flask_sqlalchemy.BaseQuery object at 0x111c69bd0>

>>> User.query.filter(User.person.in_(people)).all()
NotImplementedError: in_() not yet supported for relationships.  For a simple many-to-one, use in_() against the set of foreign key values.

What is the best way to get a list of Users where User.person is in that list of people?

Answer 1

As the error message helpfully tells you, you need to use in_ against the foreign keys instead:

User.query.join(User.person).filter(Person.id.in_(p.id for p in people)).all()

Since you're going to query for both anyway, might be better to do a joined load and then get the people using Python:

people = Person.query.join(Person.user).options(db.contains_eager(Person.user)).limit(3).all()
users = [p.user for p in people]

Answer 2

You can also use the generator with or_:

from sqlalchemy.sql import or_
people = Person.query.filter().limit(3)
cond = or_(*[User.person == person for person in people])
User.query.filter(cond).all()

This can be useful when you try to request records with filter of objects that have already been received, such as statuses.