Ruby implementation of SData (Sage Data) protocol. Rails plugin which enables SData syndication and publishing.

Let’s consider we want to expose the list of US presidents in SData way (this is exactly what is done in presidents application in acts_as_sdata-examples repository).

From client side it will look like this:

http://localhost:3000/presidents/!Wilson

<?xml version="1.0" encoding="UTF-8"?>
<entry xmlns="http://www.w3.org/2005/Atom" xmlns:attributes="http://sdata.sage.com/schemes/attributes">
  <title>Wilson, Woodrow</title>
  <summary>Wilson, Woodrow (1856-1924)</summary>
  <attributes:born_at>1856</attributes:born_at>
  <attributes:id>28</attributes:id>
  <attributes:first_name>Woodrow</attributes:first_name>
  <attributes:last_name>Wilson</attributes:last_name>
  <attributes:party>Democrat</attributes:party>
  <attributes:updated_at>Sat Jan 09 11:43:11 UTC 2010</attributes:updated_at>
  <attributes:died_at>1924</attributes:died_at>
  <attributes:order>28</attributes:order>
  <attributes:term_started_at>1913</attributes:term_started_at>
  <attributes:created_at>Sat Jan 09 11:43:11 UTC 2010</attributes:created_at>
  <attributes:country>USA</attributes:country>
  <attributes:term_ended_at>1921</attributes:term_ended_at>
</entry>

http://localhost:3000/presidents

<?xml version="1.0" encoding="UTF-8"?>
<feed xmlns="http://www.w3.org/2005/Atom">
  <id>urn:uuid:60a76c80-d399-11d9-b93C-0003939e0af6</id>
  <title>List of US presidents</title>
  <updated>2009-11-17T10:55:28+06:00</updated>
  <link href="http://example.com/presidents"/>
  <author>
    <name>Sage</name>
  </author>
  <entry>
    <title>Washington, George</title>
    <summary>Washington, George (1732-1799)</summary>
  </entry>
  <entry>
    <title>Adams, John</title>
    <summary>Adams, John (1735-1826)</summary>
  </entry>
.....

http://localhost:3000/presidents(born_at gt 1900)

<?xml version="1.0" encoding="UTF-8"?>
<feed xmlns="http://www.w3.org/2005/Atom">
  <id>urn:uuid:60a76c80-d399-11d9-b93C-0003939e0af6</id>
  <title>List of US presidents</title>
  <updated>2009-11-17T10:58:15+06:00</updated>
  <link href="http://example.com/presidents"/>
  <author>
    <name>Sage</name>
  </author>
  <entry>
    <title>Kennedy, John</title>
    <summary>Kennedy, John (1917-1963)</summary>
  </entry>
  <entry>
    <title>Johnson, Lyndon</title>
    <summary>Johnson, Lyndon (1908-1973)</summary>
  </entry>
.....

SData protocol supports data publishing (as Atom Publishing Protocol does)

Example:

require 'atom/pub'

collection = Atom::Pub::Collection.new(:href => 'http://localhost:3000/presidents')

entry = Atom::Entry.load_entry <<XML
<?xml version="1.0" encoding="UTF-8"?>
<entry xmlns="http://www.w3.org/2005/Atom" xmlns:attributes="http://sdata.sage.com/schemes/attributes">
  <attributes:born_at>1961</attributes:born_at>
  <attributes:first_name>Barack</attributes:first_name>
  <attributes:last_name>Obama</attributes:last_name>
  <attributes:party>Democrat</attributes:party>
  <attributes:died_at/>
  <attributes:order>44</attributes:order>
  <attributes:term_started_at>2009</attributes:term_started_at>
  <attributes:country>USA</attributes:country>
  <attributes:term_ended_at/>
</entry>
XML

collection.publish entry

The response will be:

<?xml version="1.0" encoding="UTF-8"?>
<entry xmlns="http://www.w3.org/2005/Atom" xmlns:attributes="http://sdata.sage.com/schemes/attributes">
  <attributes:id>46</attributes:id>
  <attributes:created_at>Sat Jan 09 14:29:57 UTC 2010</attributes:created_at>
  <attributes:first_name>Barack</attributes:first_name>
  ...
</entry>

with status 201 (Created)

(Usher is an alternative router)

It is better to refer to Usher’s page, but usually installation of Usher plugin is just one commad:

$ script/plugin install git://github.com/joshbuddy/usher.git

$ script/plugin install git://github.com/DanielVartanov/acts_as_sdata.git

In order to make application act as SData you should write the following.

map.sdata_resource :presidents
this line will enable all SData-related paths for /presidents

Also you should include special routing delimiters which are used in SData paths (remember, we are using Usher, this will NOT work with native Rails Router).

Change
ActionController::Routing::Routes.draw do |map|
to
ActionController::Routing::Routes.draw(:delimiters => ['/', '.', '!', '\(', '\)' ]) do |map|

acts_as_sdata :model => President,
              :feed => { :id => 'urn:uuid:60a76c80-d399-11d9-b93C-0003939e0af6',
                          :author => 'Sage',
                          :path => '/presidents',
                          :title => 'List of US presidents' }

:feed options defines fields of Atom feed

acts_as_sdata :title => lambda { "#{last_name}, #{first_name}" },
              :summary => lambda { "#{last_name}, #{first_name} (#{born_at}-#{died_at})" },
              :instance_id => :last_name

Note #1: these lambda’s will be executed in context of the actual model instance.

Note #2: SData specifications say that human-readable instance id’s are preferred. The :instance_id option helps to enable search by any unique attribute.

In config/initializers/mime_types.rb add the following:

ActionController::Base.param_parsers[Mime::Type.lookup('application/atom+xml')] = Proc.new do |data|
  { :entry => Atom::Entry.load_entry(data) }
end

There is an ambigious path in case of exposing same resource in both REST and SData ways:

/presidents

It might be treated either as #index (REST way) or as #sdata_collection (SData way).

In order to remove this ambiguity, a :formatted_paths option can be given as a second parameter to #sdata_resource in routes.rb:

map.sdata_resource :presidents, :formatted_paths => true

Then,
/presidents routes to Presidents#index and returns HTML
/presidents.sdata routes to Presidents#sdata_collection and returns Atom/XML

without any changes in the controller code!

Copyright Sage 2009
Released under the MIT license