find all that are nil in the association

Question

So I have a Post and a User.
Post has_many users and a user belongs_to a post.
I need a find that will find all the Posts that dont have any users like the following:

Answer 1

If you need something that is fast, employ a SQL statement like:

SELECT * 
FROM posts p 
LEFT OUTER JOIN users u ON p.id = u.post_id 
WHERE u.id IS null