CODEWITHSUNDEEP
pythonflasksqlalchemy
alphanumeric
alphanumeric

Reputation: 19329

How to query many to many using Flask SQLAlchemy

With Flask and SQLAlchemy imported:

from flask import Flask
from flask_sqlalchemy import SQLAlchemy

I go ahead and declare app and db objects:

app = Flask(__name__)
app.config['SQLALCHEMY_DATABASE_URI'] = 'sqlite:///inquestion.db' 
db = SQLAlchemy(app)

I proceed creating three Tables: Genre, Album and Artist. Since Artist can be linked to multiple Albums and Albums can include multiple Artists I need many to many attribute so there will be fourth table used to store Artist to Album ids:

albums_to_artists_table = db.Table('albums_to_artists_table',
                          db.Column('album_id', db.Integer, db.ForeignKey('album.id')),
                          db.Column('artist_id', db.Integer, db.ForeignKey('artist.id')))

class Genre(db.Model):
    id = db.Column(db.Integer, primary_key=True)
    name = db.Column(db.String(80), unique=True)

class Album(db.Model):
    id = db.Column(db.Integer, primary_key=True)
    name = db.Column(db.String(50))
    artists = db.relationship('Artist', backref='album', lazy='dynamic', secondary=albums_to_artists_table)

class Artist(db.Model):
    id = db.Column(db.Integer, primary_key=True)
    name = db.Column(db.String(80), unique=True)
    genre_id = db.Column(db.Integer, db.ForeignKey('genre.id'))

    _albums = db.relationship('Album', secondary=albums_to_artists_table, backref=db.backref('albums_to_artists_table_backref', lazy='dynamic'))

Finally I create the database:

db.drop_all()
db.create_all()

genre = Genre(name='Disco')
db.session.add(genre)
db.session.commit()

album1 = Album(name='Main Course')
album2 = Album(name='Spirits Having Flown')
db.session.add(album1)
db.session.add(album2)
db.session.commit()

artist = Artist(name='Bee Gees', genre_id = genre.id, _albums=[album1, album2])
db.session.add(artist)
db.session.commit()

Now I can query what Artists are connected to a given Genre:

Artist.query.filter_by(genre_id = genre.id).all()

I can also query what Albums the Artist is connected to:

Album.query.filter(Album.artists.any(name='Bee Gees')).all()

But how do I query what Artists are connected to a given Genre? By other words, I want to collect all the Artists linked to a Genre with a given genre.id?

Upvotes: 1

Views: 1063

Answers (1)

AArias
AArias

Reputation: 2568

But how do I query what Artists are connected to a given Genre? By other words, I want to collect all the Artists linked to a Genre with a given genre.id?

You gave an example in your question for doing exactly that, get Artist by Genre. I reckon that what you actually meant to ask is how to get Album by Genre, is that right? if so, try something like this:

Album.query.join(Artist).join(Genre).filter(Genre.id==YOUR_GENRE_ID).all()

Upvotes: 1

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