Convert SQL query to SQLAlchemy query - sqlalchemy

Question

I have two SQLALchemy models with a many-to-many relationship between them:
class Contact(db.Model):
id = db.Column(db.Integer, primary_key=True)
customer_id = db.Column(db.Integer)
users = db.relationship(ContactUser, cascade='all, delete-orphan')
class User(db.Model):
id = db.Column(db.Integer, primary_key=True)
class ContactUser(db.Model):
contact_id = db.Column(db.Integer, db.ForeignKey('contact.id'),
primary_key=True)
user_id = db.Column(db.Integer, db.ForeignKey('user.id'),
primary_key=True)
user = db.relationship(User)
I want to convert this SQL:
SELECT
c.*
FROM
contact c LEFT JOIN
user_contact uc ON c.id = uc.contact_id AND uc.user_id='456'
WHERE
c.customer_id = '123' AND
uc.contact_id IS NULL
Into an SQLAlchemy query, where I can specify customer_id and user_id.
I can't figure out how to tell SQLAlchemy to add the AND uc.user_id='456' to the ON clause.
Current query:
contacts = (Contact.query.join(ContactUser)
.filter(Contact.customer_id == customer.id)
.filter(ContactUser.contact_id == None)
The docs mention something about being able to use a "two argument calling of join", but it seems that only allows me to specify one thing, and I need two in my ON clause.
Also, I think I need to use outerjoin instead of join?

Answer 1

With the help of the guys in #sqlalchemy, we came up with:
from sqlalchemy import and_
...
Contact.query.filter(
Contact.customer_id==customer_id)
.outerjoin(ContactUser, and_(Contact.id==ContactUser.contact_id,
ContactUser.user_id!=user_id))
.filter(ContactUser.contact_id == None))