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

Learned this one just today:

Post.eager_load(:users).merge(User.where(id: nil))

Works with Rails 4+ at least.

Update:

In Rails 5+, you can use left_joins instead:

Post.left_joins(:users).merge(User.where(id: nil))