cascading_fields.py

from flask import Flask
from flask_admin import Admin
from flask_admin.contrib import sqla
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)

# Create admin app
admin = Admin(app, name="Cascade Accessories", template_mode='bootstrap3')


# Flask views
@app.route('/')
def index():
    return '<a href="/admin/">Click me to get to Admin!</a>'


class Activity(db.Model):
    __tablename__ = 'activity'
    actid = Column(Integer, primary_key=True)
    activity = Column(String(20), nullable=False, unique=True)
    accessory = relationship('Accessory', backref='activity')
    event = relationship('Event', backref='activity')


    def __str__(self):
        return self.activity


class Accessory(db.Model):
    __tablename__ = 'accessory'
    accid = Column(Integer, primary_key=True)
    actid = Column(ForeignKey('activity.actid', ondelete='CASCADE', onupdate='CASCADE'), nullable=False)
    accessory = Column(String(20), nullable=False, unique=True)
    eventaccessory = relationship('EventAccessory', backref='accessory')
    inline_models = (Activity,)

    def __str__(self):
        return self.accessory


class Event(db.Model):
    __tablename__ = 'event'
    eid = Column(Integer, primary_key=True)
    actid = Column(ForeignKey('activity.actid', ondelete='CASCADE', onupdate='CASCADE'), nullable=False)
    event = Column(String(20), nullable=False, index=True)
    eventaccessory = relationship('EventAccessory', backref='event')
    inline_models = (Activity,)

    def __str__(self):
        return self.event


class EventAccessory(db.Model):
    __tablename__ = 'eventaccessory'

    evaccid = Column(Integer, primary_key=True)
    eid = Column(ForeignKey('event.eid', ondelete='CASCADE', onupdate='CASCADE'), nullable=False)
    accid = Column(ForeignKey('accessory.accid', ondelete='CASCADE', onupdate='CASCADE'), nullable=False)
    notes = Column(String(80), nullable=False)
    inline_models = (Event, Accessory)


    def __str__(self):
        return self.notes


class AccessoryAdmin(sqla.ModelView):
    column_list = ('activity', 'accessory')
    column_editable_list = column_list


class EventAdmin(sqla.ModelView):
    column_list = ('activity', 'event')
    column_editable_list = column_list



class EventAccessoryAdmin(sqla.ModelView):
    column_list = ('event', 'accessory', 'notes')
    column_editable_list = column_list
    pass


admin.add_view(EventAccessoryAdmin(EventAccessory, db.session))

# More submenu
admin.add_view(sqla.ModelView(Activity, db.session, category='See Other Tables'))
admin.add_view(AccessoryAdmin(Accessory, db.session, category='See Other Tables'))
admin.add_view(EventAdmin(Event, db.session, category='See Other Tables'))


if __name__ == '__main__':

    db.drop_all()
    db.create_all()
    db.session.add(Activity(actid=1, activity='Swimming'))
    db.session.add(Activity(actid=2, activity='Tennis'))
    db.session.commit()
    db.session.add(Accessory(accid=1, actid=1, accessory='swimming suit'))
    db.session.add(Accessory(accid=2, actid=1, accessory='goggles'))
    db.session.add(Accessory(accid=3, actid=2, accessory='racket'))
    db.session.add(Accessory(accid=4, actid=2, accessory='shorts'))
    db.session.add(Event(eid=1, actid=1, event='The Big Swim'))
    db.session.add(Event(eid=2, actid=2, event='Wimbledon'))
    db.session.commit()
    db.session.add(EventAccessory(evaccid=1, eid=1, accid=1, notes='Get all sizes' ))
    db.session.add(EventAccessory(evaccid=2, eid=2, accid=3, notes='Large rackets only' ))
    db.session.commit()



    # Start app
    app.run(debug=True)

Accompanies this request.