SQLAlchemy Many-to-One relationship and cascade example

models.py

class Image(db.Model):
    id = db.Column(db.Integer, primary_key=True)
    url = db.Column(db.String(255))


class ThingWithImage(db.Model):
    id = db.Column(db.Integer, primary_key=True)
    image_id = db.Column(db.Integer, db.ForeignKey("image.id"))
    
    image = db.relationship("Image", foreign_keys=[image_id])


class ThingWithMultipleImages(db.Model):
    id = db.Column(db.Integer, primary_key=True)
    image_id = db.Column(db.Integer, db.ForeignKey("image.id"))
    logo_id = db.Column(db.Integer, db.ForeignKey("image.id"))

    image = db.relationship("Image", foreign_keys=[image_id])
    logo = db.relationship("Image", foreign_keys=[logo_id])

    def delete(self, commit=True):
        # TODO: Would be nice if unused Image objects could be removed as well
        if self.image:
            # This probably fails if some other object has a foreign key pointing to self.image's entry
            db.session.delete(self.image)
        if self.logo:
            # Same problem as with self.image
            db.session.delete(self.logo)
        db.session.delete(self)
        commit and db.session.commit()