title: Find all record without association with a certain field
body: <p>My question is very similar to this question: <a href="https://stackoverflow.com/questions/5319400/want-to-find-records-with-no-associated-records-in-rails-3">Want to find records with no associated records in Rails 3</a></p>
  
  <p>But with a twist. Let's use their example and add my problem:</p>
  
  <pre><code>class Person
     has_many :friends
  end
  
  class Friend
     belongs_to :person
     attr_accessor :type # this can be 'best' or 'acquaintance'
  end
  </code></pre>
  
  <p>I want to get all people without 'best' friends. The normal query for most cases that I see is to get people without any friends. And that would be:</p>
  
  <pre><code>Person.includes(:friends).where( :friends =&gt; { :person_id =&gt; nil } )
  </code></pre>
  
  <p>But that's not what I want. Is there a way to get all people who have no 'best' friends regardless of how many other type of friends they have?</p>