Hello, I have a system with users that can subscribe to other users. This is being modeled using many_to_many, the schemas look as below:

schema “users” do
    many_to_many :subscribers, User,
        join_through: UserSubscriber, 
        join_keys: [target_id: :id, subscriber_id: :id]

    many_to_many :subscriptions, User,
        join_through: UserSubscriber, 
        join_keys: [subscriber_id: :id, target_id: :id]
end

schema “users_subscribers” do
    belongs_to :target, User
    belongs_to :subscriber, User
end

My question is: Given a user, Bob, how can I fetch all users that Bob is not subscribed to? I wish to present Bob with a form where he may search for users he’s not yet subscribed to. Is there an easy way to query this in ecto or is raw sql required?