SQALCHEMY - query filtering by attribute and user_id - flask-sqlalchemy

Question

I have a User model, and a Playlist model, which references user_id as a foreign key
models.py
class User(db.Model):
__tablename__ = 'users'
id = db.Column(db.Integer, primary_key=True, autoincrement=True)
playlists = db.relationship("Playlist",
backref=db.backref('user'),
uselist=True)
def serialize(self):
"""Return object data in easily serializeable format"""
return {
'id': self.id,
'playlists' : self.playlists}
class Playlist(db.Model):
"""
Model for storing playlist information belonging to a specific user
"""
__tablename__ = 'playlist'
id = db.Column(db.Integer, primary_key=True)
title = db.Column(db.String(50))
user_id = db.Column(db.Integer, db.ForeignKey('users.id'))
#property
def serialize(self):
"""Return object data in easily serializeable format"""
return {
'id' : self.id,
'created' : self.created,
'title': self.title,
}
methods.py
def Upload_Tracks(dataset):
try:
playlist = Playlist.query.filter(Playlist.title == 'Cache').first()
if not playlist:
# create one
playlist = Playlist(title='Cache',
user=User.query.get(1))
db.session.add(playlist)
db.session.commit()
db.session.commit()
else:
playlist = Playlist.query.filter(
and_(Playlist.title == 'Cache', User.id == 1)).first()
# handler errors
except (exc.IntegrityError, ValueError):
db.session.rollback()
return {"status": True}
At first iteration of, playlist is created ADDED NEW <Playlist 'Cache'>, but at second iteration, when code reaches else, I'm getting AttributeError: 'NoneType' object for playlist here:
playlist = Playlist.query.filter(
and_(Playlist.title == 'Cache', User.id == 1)).first()
If I query filtering only one attribute, like so:
playlist = Playlist.query.filter(
(Playlist.title == 'Cache')).first()
it works.
So how do I query playlist by title AND user_id at the same time?

Answer 1

You get the above error because you tried to call User.id attribute but you didn't join that model (table) with Playlist model (table).
SQL has JOINs to join two tables (LEFT, RIGHT, INNERJOIN ...).
SQLAlchemy which you use handle this raw SQL by using join method.
So you have to use join() method to join two tables (models).
playlist = Playlist.query.join(User, User.id == Playlist.user_id).filter(
and_(Playlist.title == 'Cache', User.id == 1)).first()
You will get playlist as None (if there is no row like this in db) or Object if there is row like this.