Python: factoryboy + sqlalchemy. SubFactory and RelatedFactory example

factories.py

# factories
class CategoryFactory(factory.alchemy.SQLAlchemyModelFactory):
    class Meta:
        model = models.Category
        sqlalchemy_session = db.session
        sqlalchemy_session_persistence = 'commit'

    name = factory.Sequence(lambda n: u'Category %d' % n)

class CompanyFactory(factory.alchemy.SQLAlchemyModelFactory):
    class Meta:
        model = models.Company
        sqlalchemy_session = db.session
        sqlalchemy_session_persistence = 'commit'

    name = factory.Sequence(lambda n: u'Company %d' % n)

class ProductFactory(factory.alchemy.SQLAlchemyModelFactory):
    class Meta:
        model = models.Product
        sqlalchemy_session = db.session
        sqlalchemy_session_persistence = 'commit'

    name = factory.Sequence(lambda n: u'Name %d' % n)
    maker = factory.SubFactory(CompanyFactory)
    category1 = factory.RelatedFactory(ProductCategoryFactory, 'product')
    category2 = factory.RelatedFactory(ProductCategoryFactory, 'product')

class ProductCategoryFactory(factory.alchemy.SQLAlchemyModelFactory):
    class Meta:
        model = models.ProductCategoryFactory
        sqlalchemy_session = db.session
        sqlalchemy_session_persistence = 'commit'

    category = factory.SubFactory(CategoryFactory)
    product = factory.SubFactory(ProductFactory)

# SubFactory:
# Product has one maker that is a Company
# Reference from product to company, then SubFactory in ProductFactory


# RelatedFactory:
# Each product is associated with multiple categories
# for each realated category RelatedFactory creates a ProductCategoryFactory 
# and sets prc.product to the product being built

# Example:
# ProductFactory().create() creates 
#   - a product, lets name it P
#   - a Company and sets it as the product maker, because of `maker = factory.SubFactory(CompanyFactory)`
#   - 2 ProductCategoryFactory with .product = P, because  of `factory.RelatedFactory(ProductCategoryFactory, 'product')`
#   - 2 Categories, one for each ProductCategoryFactory, because  of `category = factory.SubFactory(CategoryFactory)`

models.py

# models
class Category(db.Model):
    __tablename__ = "category"
    id = db.Column(db.Integer, primary_key=True, autoincrement=True)
    name = db.Column(db.Unicode(255), nullable=False, unique=True)
    products = db.relationship("Product", secondary="product_category")

class Company(db.Model):
    __tablename__ = "company"
    id = db.Column(db.Integer, primary_key=True, autoincrement=True)
    name = db.Column(db.Unicode(255), nullable=False, unique=True)
    products = db.relationship("Product", back_populates="maker")


class Product(db.Model):
    __tablename__ = "product"
    id = db.Column(db.Integer, primary_key=True, autoincrement=True)
    name = db.Column(db.Unicode(255), nullable=False, unique=True)
    maker_id = db.Column(db.Integer, db.ForeignKey('company.id'), nullable=False)
    maker = db.relationship("Company", back_populates="products")
    categories = db.relationship("Category", secondary="product_category")


class ProductCategory(db.Model):
    __tablename__ = "product_category"
    product_id = db.Column(db.Integer, db.ForeignKey('product.id'), primary_key=True)
    category_id = db.Column(db.Integer, db.ForeignKey('category.id'), primary_key=True)
    product = db.relationship("Product", backref=db.backref("product_category", cascade="all, delete-orphan"))
    category = db.relationship("Category", backref=db.backref("product_category", cascade="all, delete-orphan"))