title: Searchkick Multiple Model Query
body: <p>I'm trying to run a query to find all items in a given location. I have an <code>Item.rb</code> &amp; <code>Location.rb</code> models where <code>searchkick</code> is present. In my <code>items</code> controller I have the following logic:</p>
  
  <pre><code>if params[:item_name].present?
      @items = Item.search(params[:query], index_name: [Item.searchkick_index.item_name, Location.searchkick_index.city])
  </code></pre>
  
  <p>(<code>:item_name</code> is used to catch the paramaters)</p>
  
  <p>Ant the following is the log:</p>
  
  <pre><code>Parameters: {"utf8"=&gt;"✓", "item_name"=&gt;"test", "city"=&gt;"Memphis", "commit"=&gt;"Search"}
    User Load (0.2ms)  SELECT  "users".* FROM "users" WHERE "users"."id" = ? LIMIT 1  [["id", 12]]
    CACHE (0.0ms)  SELECT  "users".* FROM "users" WHERE "users"."id" = ? LIMIT 1  [["id", 12]]
  Completed 500 Internal Server Error in 3ms
  
  NoMethodError (undefined method `item_name' for #&lt;Searchkick::Index:0x007fb43858d4e8&gt;):
  app/controllers/items_controller.rb:9:in `index'
  
  Rendered /Library/Ruby/Gems/2.0.0/gems/web-console-2.0.0.beta3/lib/action_dispatch/templates/rescues/_source.erb (12.4ms)
  Rendered /Library/Ruby/Gems/2.0.0/gems/web-console-2.0.0.beta3/lib/action_dispatch/templates/rescues/_trace.html.erb (5.6ms)
  Rendered /Library/Ruby/Gems/2.0.0/gems/web-console-2.0.0.beta3/lib/action_dispatch/templates/rescues/_request_and_response.html.erb (1.4ms)
  Rendered /Library/Ruby/Gems/2.0.0/gems/web-console-2.0.0.beta3/lib/action_dispatch/templates/rescues/_web_console.html.erb (1.3ms)
  Rendered /Library/Ruby/Gems/2.0.0/gems/web-console-2.0.0.beta3/lib/action_dispatch/templates/rescues/diagnostics.html.erb within rescues/layout (51.0ms)
  </code></pre>
  
  <p>I've tried re-indexing Location and Item, restarting the server, to no avail.</p>
  
  <p>How does one build search over two/n models ? </p>