title: Problems using pg_search with a polymorphic association
body: <p>I have the following scope for my model:</p>
  
  <pre><code>class Cloth &lt; ActiveRecord::Base
    include Ownerable
    has_many :cloth_tags, :dependent =&gt; :destroy
  
    pg_search_scope :full_search,
      associated_against: {
        cloth_tags: [:name, :brand_name]
      },
      against: [:name, :description],
      ignoring: :accents,
      using: {
        tsearch: {
          dictionary: "spanish",
          any_word: true
        }
      }
  </code></pre>
  
  <p>So if I call something like <code>Cloth.full_search('shirt')</code> works fine, but if I add <code>owner: [:name]</code> to the <code>associated_against</code> hash, it throws <code>NameError: uninitialized constant Cloth::Owner</code>. Nedless to say that the owner relationship in normal circumstances is working. In any case is defined in a module like this:</p>
  
  <pre><code>module Ownerable
  
    extend ActiveSupport::Concern
  
    included do
      belongs_to :owner, :polymorphic =&gt; true
    end
  </code></pre>
  
  <p>Any clue what thing could be? Thanks in advance</p>