Advanced Rails Recipes « Sean Mountcastle

Advanced Rails Recipes

23 Feb, 2008 Miscellaneous

Almost a year ago, I submitted three recipes to Advanced Rails Recipes. Unfortunately, one which was originally selected back in June has been dropped from the book as it’s not really advanced. So I thought I’d post it here for everyone to enjoy.

Using AJAX with REST

Problem:

You have finally mastered REST (Representational State Transfer) and wish to enhance your application with JavaScript but don’t know which of the resource URLs to call.

Ingredients:

This recipe requires Rails 1.2 or later as it relies on RJS for the Ajax portion and REST for the controller design.

Solution:

In this example we need users to be able to register (and unregister) for meetings so that we can properly report attendance. So we have three models: User, Meeting and Registration.

Since Registrations are associated with a specific meeting, we’ve created them as a nested resource, like so:

 
  map.resources :meetings do |meetings|
    meetings.resources :registrations
  end
 

To register for a meeting we want to create a new Registration instance tied to the Meeting and User. Unregistering from a meeting should destroy the Registration object. So our RegistrationsController looks like this:

 
  # POST /registrations
  def create
    @meeting = Meeting.find(params[:meeting_id])
    current_user.register_for(@meeting)
    respond_to do |format| 
      format.html { redirect_to meetings_url }
      format.js   # create.rjs
      format.xml  { head :ok }
    end
  end
 
  # DELETE /registrations/1
  def destroy
    @registration = Registration.find(params[:id])
    @registration.destroy
    respond_to do |format|
      format.html { redirect_to meetings_url }
      format.js   # destroy.rjs
      format.xml  { head :ok }
    end
  end
 

In the view we want to use Ajax to allow the user to modify their registration, so we need to use link_to_remote:

 
  <% if !current_user.registered_for(meeting) -%>
    <%= link_to_remote "Register!", :url => registrations_path(meeting), 
                                  :meeting_id => meeting.id, :method => :post %>
  <% else -%>
    <%= link_to_remote "Unregister", 
                                  :url => registration_path(meeting, 
                                             current_user.registration_for(meeting)),  
                                  :confirm => ‘Are you sure?’, :method => :delete %>
  <% end -%>
 

The RJS to update the page looks like this:

 
page[" meeting_#{@meeting.id}".to_sym].replace_html 
       :partial => ’shared/meeting’, :object => @meeting
page[" meeting_#{@meeting.id}".to_sym].visual_effect :highlight, :duration => 5
 

Discussion:

The resource URLs provided by Rails are extremely useful, but they can be confusing. Tools like FireBug make it easy to see what is going on behind the scenes. When developing Rails applications, it is usually easier to develop without Ajax and then go back and add Ajax to those portions of the application where it would make sense. With this approach, you can gracefully degrade your service back to the original mode for those who don’t have or don’t enable JavaScript. It also allows you to click through your application with FireBug enabled and watch which URLs are hit and with which methods (GET, POST, PUT, or DELETE).

The table below outlines which resource URLs to use with your remote helpers:

Intent	Action	Resource URL	Method
Creating a new instance	create	plural form of model name (i.e. registrations_path)	POST
Retrieving an instance	show	singular form of model name with id (i.e. registration_path(registration)	GET
Retrieving all instances	index	plural form of model name (i.e. registrations_path)	GET
Modifying an existing instance	update	singular form of model name with id (i.e. registration_path(registration))	PUT
Deleting an existing instance	destroy	singular form of model name with id (i.e. registration_path(registration))	DELETE

Once you are comfortable with the resource URLs, adding Ajax to your RESTful is much easier.

Sean Mountcastle