title: ActiveRecord - Avoiding record instantitation while looking up many to many relation
body: <p>I have two models in my Rails 6 / PostgreSQL application which have a many to many relation; <code>Car</code> and <code>Driver</code>. The goal is to get all records (Cars) which have no association at all (Drivers). At the moment this is done using Ruby (2.6.3) like this:</p>
  
  <pre><code>result = []
  Car.all.each do |car|
    result &lt;&lt; car.id if car.drivers.empty?
  end
  </code></pre>
  
  <p>Is there an ActiveRecord expression which avoids instantiating each record?</p>