Display Users without Posts in Rails

Question

How would I query my Users who have yet to write any posts? This is what I am trying:

u = User.joins(:posts).where('posts.size = ?', 0)

Output:

PG::UndefinedColumn: ERROR:  column posts.size does not exist

Trying to wrap my head around the correct SQL syntax, but no luck so far

Answer 1

You must do this without a join, like this:

 User.where(Post.where("posts.user_id = users.id").exists.not)

Its very useful to chain conditions (like applying different filters).

---

creates SQL like:

SELECT "users".* FROM "users"  
WHERE (
  NOT (
    EXISTS (SELECT "posts".* FROM "posts"  WHERE (posts.user_id = users.id))
  )
)