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

something like that:

p = Post.arel_table
u = User.arel_table

posts = Post.find_by_sql(p.join(u).on(p[:user_id].eq(u[:p_id])).where(u[:id].eq(nil)).to_sql)