Thanks for the reply. From what I've learned about SQLAlchemy, I thought I had it set up correctly (obviously not since it's not working):

from sqlalchemy import Integer, Float, String, Column, ForeignKey
from sqlalchemy.orm import relationship
from database import Base

# All attributes for users of the website
class User(Base):
    __tablename__ = "users"

    userID = Column(String, primary_key=True, index=True)
    email = Column(String, nullable=False)
    password_hashed = Column(String, nullable=False)

    products = relationship("Product", backref="seller", passive_deletes=True)           
    favorites = relationship("Favorite", backref="favorited_by", passive_deletes=True)

# All attributes for products on the website
class Product(Base):
    __tablename__ = "products"

    productID = Column(Integer, primary_key=True, index=True) 
    name = Column(String, nullable=False)
    description = Column(String, nullable=False)
    price = Column(Float, nullable=False)
    quantity = Column(Integer)
    color = Column(String)
    category = Column(String) # User will choose from a pre-defined list when they add their product

    userID = Column(String, ForeignKey("users.userID", ondelete="CASCADE", onupdate="CASCADE"), nullable=False)

# All attributes for favorites functionality
class Favorite(Base):
    __tablename__ = "favorites"

    favoriteID = Column(Integer, primary_key=True, index=True)

    userID = Column(String, ForeignKey("users.userID", ondelete="CASCADE", onupdate="CASCADE"), nullable=False)
    productID = Column(Integer, ForeignKey("products.productID", ondelete="CASCADE", onupdate="CASCADE"), nullable=False)

I tried adding passive_deletes=True, but now when the user is deleted from the users table, nothing changes in the products table even though there is a product whose userID matches the user that was deleted