[sqlalchemy] "AssertionError: Dependency rule tried to blank-out primary key column" with Elixir

[kremlan]

I've posted the following question on the Elixir group and they sent
me here.

My setup

##
# Tables
##
roles = Table('roles', meta,
    Column('id', Integer, primary_key=True),
    Column('name', String(25))
)

users = Table('users', meta,
    Column('id', Integer, primary_key=True),
    Column('username', String(125)),
    Column('password', String(125)),
    ....
)

users_roles = Table('users_roles', meta,
    Column('user_id', Integer, primary_key=True),
    Column('role_id', Integer, primary_key=True),
    ....
    ForeignKeyConstraint(['user_id'], ['users.id']),
    ForeignKeyConstraint(['role_id'], ['roles.id'])
)

##
# Elixir models
##

class UserRole(Entity):
    using_options(tablename='users_roles', autoload=True)
    user = ManyToOne('User', colname='user_id')
    role = ManyToOne('Role', colname='role_id')

class Role(Entity):
    using_options(tablename='roles', autoload=True)
    users_roles = OneToMany('UserRole')
    users = AssociationProxy('users_roles', 'user')

class User(Entity):
    using_options(tablename='users', autoload=True)
    users_roles = OneToMany('UserRole')
    roles = AssociationProxy('users_roles', 'role')

This setup works fine for reading but not for updating or deleting.

I was able to then get the append method working via the following

def _create_ur_by_role(role):
    return UserRole(role=role)

in class User:
roles = AssociationProxy('users_roles', 'role',
creator=_create_ur_by_role)

I am still unable to delete roles. Example:
me.roles.pop()    < -- works fine
session.flush()

results in...

AssertionError: Dependency rule tried to blank-out primary key column
'users_roles.user_id'

I have tried adding ondelete='cascade' to the UserRole model. This
caused no change.

Any help will be greatly appreciated

-brad

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