mock-alchemy: how to handle foreign-key/relationship

Question

How can I mock the foreign-key/relationship correctly with the mock-alchemy package? The "content" object has no "content_type_config"

import unittest
from sqlalchemy import Column, String, Integer, ForeignKey
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.orm import relationship
from alchemy_mock.mocking import UnifiedAlchemyMagicMock

Base = declarative_base()


class content_type_config(Base):
    __tablename__ = 'content_type_config'
    type_id = Column("type_id", Integer, primary_key=True)
    name = Column("name", String(255))

    def __init__(self, type_id, name):
        self.type_id = type_id
        self.name = name


class content(Base):
    __tablename__ = 'content'
    id = Column("id", Integer, primary_key=True)
    name = Column("name", String(255))
    f_type_id = Column("f_type_id", Integer, ForeignKey("content_type_config.type_id", name="content_f_type_id_fkey"))

    content_type_config = relationship('content_type_config',
                                       primaryjoin="content.f_type_id == content_type_config.type_id", 
                                       foreign_keys="[content.f_type_id]")

    def __init__(self, id, name, f_type_id):
        self.id = id
        self.name = name
        self.f_type_id = f_type_id


class TestSomething(unittest.TestCase):

    def test_one(self):
        session = UnifiedAlchemyMagicMock()
        session.add(content_type_config(1, 'Name for type 1'))
        session.add(content(1, 'TheName', 1))

        res = session.query(content).all()

        print(res[0].content_type_config)

    def tearDown(self):
        print('Tearing down unittest')

The printed result is None. Should be an content_type_config object