Dependency rule tried to blank-out primary key column in SQL-Alchemy when trying to delete record

Question

I have a many to one relationship between the Userownedshare table and the Share table.

When I delete a Userownedshare entry from the database I get the following error: AssertionError: Dependency rule tried to blank-out primary key column 'share.ticker'

This makes sense as the ticker field in Userownedshare is a Foreign Key in the Share table. However I cannot work out how to fix this error. I think that I want to set up a cascading deletion when a Share entry is orphaned but I cannot work out how to do this, I have read the documentation but I just end up with different types of errors so I think I am missing something trivial. Hope someone can help, thanks!

Here is my code:

class Userownedshare(db.Model):
    id = db.Column(db.Integer, primary_key=True)
    ticker = db.Column(db.String(20), db.ForeignKey('share.ticker'))
    user = db.Column(db.String, db.ForeignKey('user.username'))
    quantity = db.Column(db.Integer, nullable=False)
    dividends = db.Column(db.Float, server_default="0.0")
    triggerlevel = db.Column(db.Integer)
    smsalert = db.Column(db.Boolean)
    emailalert = db.Column(db.Boolean)
    portfolioid = db.Column(db.String(50))
    name = db.relationship('Share', backref='userownedshare' ,  foreign_keys=[ticker])

class Share(db.Model):
    id = db.Column(db.Integer)
    name = db.Column(db.String(50), nullable=False)
    ticker = db.Column(db.String(50), db.ForeignKey('userownedshare.ticker'), primary_key=True)
    tickermatch = db.relationship('Userownedshare', backref='share',  foreign_keys=[ticker])

Answer 1

OK, so after some trial and error I worked it out. I needed to add cascade="all, delete-orphan", to the tickermatch relationship in the Share class.

But I also needed to add lazy="joined" to the name relationship in the Userownedshare class

class Userownedshare(db.Model):
    id = db.Column(db.Integer, primary_key=True)
    ticker = db.Column(db.String(20), db.ForeignKey('share.ticker'))
    user = db.Column(db.String, db.ForeignKey('user.username'))
    quantity = db.Column(db.Integer, nullable=False)
    dividends = db.Column(db.Float, server_default="0.0")
    triggerlevel = db.Column(db.Integer)
    smsalert = db.Column(db.Boolean)
    emailalert = db.Column(db.Boolean)
    portfolioid = db.Column(db.String(50))
    name = db.relationship('Share', backref='userownedshare',  foreign_keys=[ticker], lazy="joined")

class Share(db.Model):
    id = db.Column(db.Integer)
    name = db.Column(db.String(50), nullable=False)
    ticker = db.Column(db.String(50), db.ForeignKey('userownedshare.ticker'), primary_key=True)
    tickermatch = db.relationship('Userownedshare', backref='share', cascade="all, delete-orphan", lazy="joined")