SQLAlchemy query, join on relationship and order by count

问题:

I have two SQLAlchemy models set up as follows:

############## # Post Model # ############## class Post(db.Model):     id = db.Column(db.Integer, primary_key = True)     title = db.Column(db.String(250))     content = db.Column(db.String(5000))     timestamp = db.Column(db.Integer)     author_id = db.Column(db.Integer, db.ForeignKey('user.id'))     likes = db.relationship('Like', backref = 'post', lazy = 'dynamic')  ############### # Likes Model # ############### class Like(db.Model):     id = db.Column(db.Integer, primary_key = True)     voter_id = db.Column(db.Integer, db.ForeignKey('user.id'))     post_id = db.Column(db.Integer, db.ForeignKey('post.id')) 

As you can see, there's a model for posts and a model for user likes on those posts. I'd like to create a query that selects all posts, ordered by the number of likes that post has. In the shell, I can run:

SELECT post.*,         count(like.id) AS num_likes FROM post LEFT JOIN like ON post.id = like.post_id GROUP BY post.id; 

What's the equivalent SQLAlchemy command?

Thanks!

回答1:

The translation from raw query to Flask-SQLAlchemy is pretty much mechanical:

db.session.query(Post, db.func.count(Like.id)).outerjoin(Like).group_by(Post.id) 

文章来源: SQLAlchemy query, join on relationship and order by count