Delete all in a Many to Many secondary table association in sqlalchemy

Question

I have following models and associations:

class CartProductsAssociation(db.Model):
    __tablename__ = 'cart_products_association'
    cart_id = db.Column(db.Integer, db.ForeignKey('carts.id',ondelete='CASCADE'),primary_key=True)
    product_id = db.Column(db.Integer, db.ForeignKey('products.id',ondelete='CASCADE'), primary_key=True)
    quantity = db.Column(db.Integer)

    product = db.relationship("Product", backref="cart_associations", cascade="all,delete",passive_deletes=True)
    cart = db.relationship("Cart", backref="product_associations",cascade="all,delete",passive_deletes=True)


class Product(db.Model):
    __tablename__ = 'products'
    id = db.Column(db.Integer, primary_key=True)
    name = db.Column(db.String)
    img_path = db.Column(db.String)

    price = db.Column(db.Float, default=0.0)

    product_categories = db.relationship(
        "ProductCategory",
        secondary=product_product_categories,
        back_populates="products")

    carts = db.relationship("Product", secondary="cart_products_association",passive_deletes=True,cascade="all,delete" )

class Cart(db.Model):
    __tablename__ = 'carts'
    id = db.Column(db.Integer, primary_key=True)

    branch_id = db.Column(db.Integer, db.ForeignKey('branch.id'))
    branch = db.relationship("Branch", back_populates="carts")

    page_id = db.Column(db.Integer, db.ForeignKey('pages.id'))
    page = db.relationship("Page", back_populates="carts")


    shopper_id = db.Column(db.String, db.ForeignKey('shoppers.fb_user_id'))
    shopper = db.relationship(
        "Shopper",
        back_populates="carts")

    products = db.relationship("Product", secondary="cart_products_association")
    cart_status = db.Column(db.Enum('user_unconfirmed','user_confirmed','client_unconfirmed','client_confirmed', name='cart_status'), default='user_unconfirmed')

When I am trying to delete a product I am getting following error: AssertionError

AssertionError: Dependency rule tried to blank-out primary key column 'cart_products_association.cart_id' on instance ''

How can I solve it?

Delete all in a Many to Many secondary table association in sqlalchemy

2 Answers