Sqlalchemy in_ subquery

Question

I am trying to implement a select with a nested select clause, to find parents without any children. My tables (radically simplified) are as follows:

class Pers         


        

Answer 1

Join worked for me. Thank you. In my case I was trying to find all ordered objects (Topics) which belong to a particular customer. I have 3 tables Customer, Order, Topics

stmt = db.session.query(Topics).outerjoin(Order).\
    filter(Order.cust_id == id)

topics = stmt.all()

Answer 2

Using a subquery:

sub_stmt = config.Session.query(ChildTable.person_id)
stmt = config.Session.query(Person).filter(~Person.id.in_(sub_stmt))
empty_persons = stmt.all()

emits the following sql:

SELECT person.id AS person_id, person.name AS person_name
FROM person
WHERE person.id NOT IN (SELECT foo.person_id AS foo_person_id
FROM foo)

Using a join:

stmt = config.Session.query(Person).outerjoin(ChildTable).filter(ChildTable.person_id.is_(None))
empty_persons = stmt.all()

emits the following sql:

SELECT person.id AS person_id, person.name AS person_name
FROM person LEFT OUTER JOIN foo ON person.id = foo.person_id
WHERE foo.person_id IS NULL

I think both achieve your desired result set.