Professional Ruby on Rails™

9.3. Producing Web Service Data

If you've set up your application using RESTful controllers, then you're already halfway toward acting as a web service. Your application is set up with a standard API that other applications will be able to hit. The second half involves producing machine-readable code in the expected formats.

9.3.1. Producing XML

You've already seen the first part of the Rails XML response mechanism — it's part of the RESTful controller scaffold. As a reminder, here it is again:

def index
    @recipes = Recipe.find(:all)
    respond_to do |format|
      format.html # index.html.erb
      format.xml  { render :xml => @recipes }
    end
  end

The render :xml method call immediately turns around and calls the to_xml method on the argument. Rails defines to_xml for most classes, including ActiveRecord::Base, Array, and Hash. For example, the default XML result for a Recipe object would look something like this:

<?xml version=\"1.0\" encoding=\"UTF-8\"?>
<recipe>
  <cached-ingredient-string></cached-ingredient-string>
  <cached-tag-list>grandma, chicken, fred</cached-tag-list>
  <created-at type=\"datetime\">2007-08-05T20:03:33-05:00</created-at>
  <description>Yummy!</description>
  <directions>Things</directions>
  <id type=\"integer\">1</id>
  <servings>3</servings>
  <title>Grandma's Chicken Soup</title>
  <updated-at type=\"datetime\">2007-09-04T23:04:45-05:00</updated-at>
  <user-id type=\"integer\">2</user-id>
</recipe>

The default XML for an array of recipes is similar, but it wraps the whole thing in a ...