SqlAlchemy and Flask, how to query many-to-many relationship

Question

I need help creating SqlAlchemy query.

I'm doing a Flask project where I'm using SqlAlchemy. I have created 3 tables: Restaurant, Dish and restaurant_dish in my models.py file.

restaurant_dish = db.Table('restaurant_dish',     db.Column('dish_id', db.Integer, db.ForeignKey('dish.id')),     db.Column('restaurant_id', db.Integer, db.ForeignKey('restaurant.id')) )  class Restaurant(db.Model):     id = db.Column(db.Integer, primary_key = True)     name = db.Column(db.String(64), index = True)      restaurant_dish = db.relationship('Dish', secondary=restaurant_dish,         backref=db.backref('dishes', lazy='dynamic'))   class Dish(db.Model):     id = db.Column(db.Integer, primary_key = True)     name = db.Column(db.String(64), index = True)     info = db.Column(db.String(256), index = True) 

I have added data to the restaurant_dish table and it should be working correctly. Where I need help is understanding how to correctly get a Dish using Restaurant. Raw SQL would be something like this:

SELECT dish_id FROM restaurant_dish WHERE restaurant_id == id 

What I have managed to get done but not working:

x = Restaurant.query.filter_by(Restaurant.restaurant_dish.contains(name)).all() 

Thanks for help and I also appreciate tutorials that can point me in the right direction(the official documentation goes over my head).

Answer 1

The semantic of the relationship doesn't look right. I think it should be something like:

class Restaurant(db.Model):     ...      dishes = db.relationship('Dish', secondary=restaurant_dish,         backref=db.backref('restaurants')) 

Then, to retrieve all the dishes for a restaurant, you can do:

x = Dish.query.filter(Dish.restaurants.any(name=name)).all() 

This should generate a query like:

SELECT dish.* FROM dish WHERE     EXISTS (         SELECT 1         FROM restaurant_dish         WHERE             dish.id = restaurant_dish.dish_id             AND EXISTS (                 SELECT 1                 FROM restaurant                 WHERE                     restaurant_dish.restaurant_id = restaurant.id                     AND restaurant.name = :name             )     )