blackrat.org

As of this post I have two classes joined by have_and_belongs_to_many (habtm), and I figured that I’d like to be able to click on an entry in one and have a subset index of the other appear. Not an uncommon task and used by tags and blogs everywhere. Rather than search for a snippet, I thought I’d give it a go myself first.What I came up with surprised me with it’s simplicity and may not be the most expedient manner, but seems to be a neat and easy extension of the index method.

The obvious way was to add an entry to the list of actions which can be applied to a tag item. A simple addition of a “Show Users” link pointing to the Users controller and passing a tag_id parameter was the starting point for this.

Opening up app/views/tags/index.rhtml, we can add a user_path with :tag_id=>tag as the parameter. This will translate to http://localhost:3000/users?tag_id=x.

<h1>Listing tags</h1>

<table>
  <tr>
    <th>Name</th>
  </tr>

<% for tag in @tags %>
  <tr>
    <td><%=h tag.name %></td>
    <td><%= link_to 'Users', user_path(:tag_id=>tag) %></td>
    <td><%= link_to 'Show', tag_path(tag) %></td>
    <td><%= link_to 'Edit', edit_tag_path(tag) %></td>
    <td><%= link_to 'Destroy', tag_path(tag), :confirm => 'Are you sure?', :method => :delete %></td>
  </tr>
  <% end %>
</table>
<br />
<%= link_to 'New tag', new_tag_path %>

This will then allow the following in the index view of the users controller.

  # GET /users
  # GET /users.xml
  def index
    @tag=Tag.find(params[:tag_id]) if params[:tag_id]
    @users = @tag.users || throw rescue User.find(:all)

    respond_to do |format|
      format.html # index.rhtml
      format.xml  { render : xml => @users.to_xml }
    end
  end

Note the unusual throw rescue construct. Since @tag.users would throw an exception, as well as having a nil possibility, this is the dryest form of getting the original User.find(:all) executed on error. I mainly wanted to see if this would work, and it does! I’m really starting to like what you can do with Ruby.