This guide should provide you with all you need to get started managing the connection between business objects and RESTful web services. It implements a way to map web-based resources to local objects with CRUD semantics.
endprologue.
WARNING. This Guide is based on Rails 3.0. Some of the code shown here will not work in earlier versions of Rails.
Active Resource allows you to connect with RESTful web services. So, in Rails, Resource classes inherited from +ActiveResource::Base+ and live in +app/models+.
Active Resource make request over HTTP using a standard JSON format. It mirrors the RESTful routing built into Action Controller but will also work with any other REST service that properly implements the protocol.
h4. Read
Read requests use the GET method and expect the JSON form of whatever resource/resources is/are being requested.
Creating a new resource submits the JSON form of the resource as the body of the request with HTTP POST method and parse the response into Active Resource object.
Module to support validation and errors with Active Resource objects. The module overrides Base#save to rescue ActiveResource::ResourceInvalid exceptions and parse the errors returned in the web service response. The module also adds an errors collection that mimics the interface of the errors provided by ActiveRecord::Errors.
h4. Validating client side resources by overriding validation methods in base class
<ruby>
class Person < ActiveResource::Base
self.site = "http://api.people.com:3000/"
protected
def validate
errors.add("last", "has invalid characters") unless last =~ /[a-zA-Z]*/
end
end
</ruby>
h4. Validating client side resources
Consider a Person resource on the server requiring both a first_name and a last_name with a validates_presence_of :first_name, :last_name declaration in the model:
<ruby>
person = Person.new(:first_name => "Jim", :last_name => "")
person.save # => false (server returns an HTTP 422 status code and errors)
person.valid? # => false
person.errors.empty? # => false
person.errors.count # => 1
person.errors.full_messages # => ["Last name can't be empty"]
person.errors[:last_name] # => ["can't be empty"]
person.last_name = "Halpert"
person.save # => true (and person is now saved to the remote service)
</ruby>
h4. Public instance methods
ActiveResource::Validations have three public instance methods
h5. errors()
This will return errors object that holds all information about attribute error messages
h5. save_with_validation(options=nil)
This validates the resource with any local validations written in base class and then it will try to POST if there are no errors.
h5. valid?
Runs all the local validations and will return true if no errors.