How to three-way many-to-many relationship in flask-sqlalchemy

Question

What\'s the proper way to design a three-way many-to-many in flask-sqlalchemy?

Assume I have users, teams and roles. Users are assigned to teams. When assigned to a team

Answer 1

dudes. There is official way to solve the problem with two many-many by using a helper table.

Helper_table = db.Table('Helper_table',
                     db.Column('id_a', db.Integer,
                               db.ForeignKey('a.id')),
                     db.Column('id_b', db.Integer,
                               db.ForeignKey('b.id'))
                )

class A(db.Model):  # A ORM
    id = db.Column(db.Integer, primary_key=True)
    username = db.Column(db.String(64), index=True, unique=True)

    bs = db.relationship(
        'B', secondary=Helper_table, lazy='dynamic')

    def __repr__(self):
        return ''.format(self.username)

class B(db.Model):  # B ORM
    id = db.Column(db.Integer, primary_key=True)
    username = db.Column(db.String(64), index=True, unique=True)


    as = db.relationship(
        'A', secondary=Helper_table, lazy='dynamic')

    def __repr__(self):
        return ''.format(self.username)

But it can only solve the two many-many problem !!! It will automatically handle the relationship.

a1 = A(username="a1_"+str(uuid.uuid4()))
b1 = B(username="b1_"+str(uuid.uuid4()))

a1.bs.append(b1)
db.session.add(a1)
db.session.commit()

As the code above shows that it will auto add b1 into database as well as b1.as.

But when I tried this method in 3 many-many-many situation, everything f**k up.

Here are the questions I asked: multi-helper table for many-many-many-... relationship in flask-sqlalchemy

Generally, I think it should be a feature of this repo. There should be an elegant way to handle it.