如何在SQLAlchemy中按关系数量选择模型，然后按相同数量排序？

Question

So I can easily select by the value of a relationship's field, but I can't for the life of me figure out how to select and order by the number of relationships. Specifically, what I want to do is select all users with at least one post, and then order by the users with the most posts. I want to do this without storing an extra field in the database as a post count, or selecting all of them and sorting them manually.

Something like

User.query.filter(len(User.posts.all()) > 0).all()

would be ideal for example, though this doesn't seem to work.

Any ideas?

Answer 1

use having()

from sqlalchemy import func

session.query(User).\
        join(User.posts).\
        group_by(User).\
        having(func.count(Post.id) > 0).\
        order_by(func.count(Post.id).desc())