title: Tire Gem Returns 'Can't sort on string types with more than one value per doc, or more than one token per field'
body: <p>I have mapped an associated field as a multi-field. I have set the 'name' property to be analyzed using a snow ball analyzer and 'exact' as not analyzed. I am able to search on this field and filter as well. I am not able to sort on this field. When trying to sort, elastic returns an error "Can't sort on string types with more than one value per doc, or more than one token per field". </p>
  
  <p>I have attempted creating an additional field called 'raw' similar to exact, and this did not work either. Below is my mapping and how I am attempting to perform the sort via the tire gem:</p>
  
  <pre><code>    mapping do
      indexes :sectors, :type =&gt; 'object',
        :properties =&gt; { :name =&gt; { :type =&gt; 'multi_field',
                                    :fields =&gt; {
                                      :name =&gt;  { :type =&gt; 'string', :analyzer =&gt; 'snowball' },
                                      :exact =&gt; { :type =&gt; 'string', :index =&gt; 'not_analyzed' , :include_in_all =&gt; false }
                                    }
                                    }
                         }
  end
  
  def to_indexed_json
      to_json( :include =&gt; {
                 ...
                 :sectors =&gt; { :only =&gt; ["name"] },
                 ...
      })
  end
  
  def self.search(params)
    tire.search(:load =&gt; true, :page=&gt;params[:page], :per_page =&gt; 12) do
  
      if params[:query].present?
        query { string params[:query], :default_operator =&gt; "OR" }
      else
        query { all }
      end
  
      filter :term, "sectors.name.exact" =&gt; params[:sector] if params[:sector].present?
      sort { by 'sectors.name.exact','asc' } if !params[:sort][:sector].blank?
    end
  end
  </code></pre>