title: Rails: Hidden field in form_for is not sending parameters to controller
body: <p>I have a <code>form_for</code> I'm making in my view helper that is going to let one user promote another user from a group.  </p>
  
  <pre><code>  def promote_button_for(group, user)
      membership = group.get_membership( user )
      form_for membership, :url =&gt; group_membership_path( group, membership ) do |f|
        f.hidden_field :group_creator
        hidden_field_tag 'test', '1'
        f.submit( "Promote", :onclick =&gt; "return confirm(\"Are you sure you want to promote #{user.email} to an officer?\")" )
      end
    end
  </code></pre>
  
  <p>When I submit the form via the button, I don't seem to get any of the hidden field parameters sending to the controller. </p>
  
  <pre><code>Started POST "/groups/1/memberships/6" for 127.0.0.1 at 2011-02-01 01:45:32 -0600
    Processing by MembershipsController#update as HTML
    Parameters: {"utf8"=&gt;"✓", "authenticity_token"=&gt;"VQl/rVX8OVOETv2HE7KtopUc3B19ShoMkUhjJwNlaZs=", "commit"=&gt;"Promote", "group_id"=&gt;"1", "id"=&gt;"6"}
  </code></pre>
  
  <p>The generated Html looks like:</p>
  
  <pre><code>&lt;form accept-charset="UTF-8" action="/groups/1/memberships/6" class="edit_membership" id="edit_membership_6" method="post"&gt;
     &lt;div style="margin:0;padding:0;display:inline"&gt;
        &lt;input name="utf8" type="hidden" value="&amp;#x2713;" /&gt;
        &lt;input name="_method" type="hidden" value="put" /&gt;
        &lt;input name="authenticity_token" type="hidden" value="VQl/rVX8OVOETv2HE7KtopUc3B19ShoMkUhjJwNlaZs=" /&gt;
     &lt;/div&gt;
     &lt;input id="membership_submit" name="commit" onclick="return confirm(&amp;quot;Are you sure you want to promote kquiring@gmail.com to an officer?&amp;quot;)" type="submit" value="Promote" /&gt;
  &lt;/form&gt;
  </code></pre>
  
  <p>Any help would be greatly appreciated,</p>
  
  <p>Thanks!</p>