title: Form_tag remote in Rails 3 in partial
body: <p>To become member, A user can use a button to create a membership on the community page. This is made on a partial that create a new "membership"
  the memberships_controller :</p>
  
  <pre><code> @community = Community.find(params[:community_id])
   @community.memberships.create(:user =&gt; current_user, :role =&gt; 1)
  </code></pre>
  
  <p>in The view :</p>
  
  <pre><code>&lt;% form_remote_tag :url =&gt; community_memberships_path(@community) do %&gt;
     &lt;%= submit_tag 'Join' %&gt;
  &lt;% end %&gt;
  </code></pre>
  
  <p><strong>After upgrading to Rails 3, that doesn't work anymore !</strong></p>
  
  <p>I tried this :</p>
  
  <pre><code>&lt;% form_tag( {:url =&gt; community_memberships_path(@community)}, :remote =&gt; true) do %&gt;
  </code></pre>
  
  <p>and this :</p>
  
  <pre><code>&lt;% form_tag :url =&gt; {:controller =&gt; '/memberships/new', :action =&gt; :create,:community_id =&gt; @community }, :remote =&gt; true do %&gt;
  </code></pre>
  
  <p>But no chance.. and have this error</p>
  
  <blockquote>
    <p>No route matches "/communities/2</p>
  </blockquote>
  
  <p>Thx for help</p>