test_delete.py

from flask import Flask
from flask_sqlalchemy import SQLAlchemy
from sqlalchemy import Column, ForeignKey, Integer, String
from sqlalchemy.orm import relationship


# Create application
app = Flask(__name__)

# Create dummy secrey key so we can use sessions
app.config['SECRET_KEY'] = '123456790'

app.config['SQLALCHEMY_DATABASE_URI'] = 'sqlite:///a_sample_database.sqlite'
app.config['SQLALCHEMY_ECHO'] = True
db = SQLAlchemy(app)


class Person(db.Model):
    __tablename__ = 'person'
    uid = Column(Integer, primary_key=True)
    username = Column(String(20), nullable=False, unique=True)

    def __str__(self):
        return self.username


class Magazine(db.Model):
    __tablename__ = 'magazine'
    mid = Column(Integer, primary_key=True)
    title = Column(String(80), nullable=False, index=True)

    def __str__(self):
        return self.title


class Subscription(db.Model):
    __tablename__ = 'subscription'

    subid = Column(Integer, primary_key=True)
    uid = Column(ForeignKey('person.uid', ondelete='CASCADE', onupdate='CASCADE'), nullable=False)
    mid = Column(ForeignKey('magazine.mid', ondelete='CASCADE', onupdate='CASCADE'), nullable=False, index=True)
    notes = Column(String(140), nullable=False)

    # need this to display in child tables (e.g. sub_schedule)
    def __str__(self):
        return self.notes


class SubscriptionSchedule(db.Model):
    __tablename__ = 'subscription_schedule'

    schedid = Column(Integer, primary_key=True)
    # The deletion also fails when you remove the CASCADE
    subid = Column(ForeignKey('subscription.subid', ondelete='CASCADE', onupdate='CASCADE'), nullable=False)
    notes = Column(String(140), nullable=False)

    subscription = relationship('Subscription', backref='subschedule')

    def __str__(self):
        return self.notes

if __name__ == '__main__':

    db.drop_all()
    db.create_all()
    db.session.add(Person(uid=1, username='Joe'))
    db.session.add(Person(uid=2, username='Ann'))
    db.session.add(Magazine(mid=1, title='Time'))
    db.session.add(Magazine(mid=2, title='Newsweek'))
    db.session.commit()

    subscription_1 = Subscription(uid=1, mid=1, subid=1, notes='Joe subscribed to Time' )
    db.session.add(subscription_1)
    subscription_2 = Subscription(uid=2, mid=2, subid=2, notes='Ann subscribed to Newsweek' )
    db.session.add(subscription_2)
    db.session.commit()

    db.session.add(SubscriptionSchedule(schedid=1, subid=1, notes="Joe's Time subscription has a schedule" ))
    db.session.commit()

    db.session.delete(subscription_1)
    db.session.commit()


    # Start app
    app.run(debug=True)