There are several ways. Here is one using a subquery:
subscribed_id_query = bob |> Ecto.assoc(:subscribers) |> select(:id)
where(User, [u], u.id not in subquery(subscribed_id_query))
This is the simplest query that comes to mind, not necessarily the most optimized. If you have specific SQL you would like to generate you should include that in your post.
