title: Rails User.joins.not(...) in Active Record?
body: <p>Im looking to query all Users without Comments in a single sql query?</p>
  
  <p>Models:</p>
  
  <pre><code>class User &lt; ActiveRecord::Base
    has_many :comments
  end
  
  class Comment &lt; ActiveRecord::Base
    belongs_to :user
  end
  </code></pre>
  
  <p>So I want the opposite of this: </p>
  
  <pre><code>User.joins.(:comments).group('users.id')
  </code></pre>
  
  <p>But not like this: (because it generates two queries)</p>
  
  <pre><code>User.where.not(id: Comment.pluck(:user_id))
  </code></pre>
  
  <p>Maybe something like this?</p>
  
  <pre><code>User.joins.not.(:comments).group('users.id')
  </code></pre>
  
  <p>Thanks for any input!</p>