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Active Resource (ARes) connects business objects and Representational State Transfer (REST)
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web services. It implements object-relational mapping for REST webservices to provide transparent
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proxying capabilities between a client (ActiveResource) and a RESTful service (which is provided by Simply RESTful routing
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in ActionController::Resources).
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Active Resource attempts to provide a coherent wrapper object-relational mapping for REST
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web services. It follows the same philosophy as Active Record, in that one of its prime aims
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is to reduce the amount of code needed to map to these resources. This is made possible
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by relying on a number of code- and protocol-based conventions that make it easy for Active Resource
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to infer complex relations and structures. These conventions are outlined in detail in the documentation
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for ActiveResource::Base.
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Model classes are mapped to remote REST resources by Active Resource much the same way Active Record maps model classes to database
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tables. When a request is made to a remote resource, a REST XML request is generated, transmitted, and the result
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received and serialized into a usable Ruby object.
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=== Configuration and Usage
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Putting ActiveResource to use is very similar to ActiveRecord. It's as simple as creating a model class
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that inherits from ActiveResource::Base and providing a <tt>site</tt> class variable to it:
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class Person < ActiveResource::Base
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self.site = "http://api.people.com:3000/"
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Now the Person class is REST enabled and can invoke REST services very similarly to how ActiveRecord invokes
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lifecycle methods that operate against a persistent store.
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# Find a person with id = 1
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Person.exists?(1) #=> true
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As you can see, the methods are quite similar to Active Record's methods for dealing with database
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records. But rather than dealing directly with a database record, you're dealing with HTTP resources (which may or may not be database records).
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Active Resource is built on a standard XML format for requesting and submitting resources over HTTP. It mirrors the RESTful routing
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built into ActionController but will also work with any other REST service that properly implements the protocol.
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REST uses HTTP, but unlike "typical" web applications, it makes use of all the verbs available in the HTTP specification:
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* GET requests are used for finding and retrieving resources.
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* POST requests are used to create new resources.
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* PUT requests are used to update existing resources.
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* DELETE requests are used to delete resources.
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For more information on how this protocol works with Active Resource, see the ActiveResource::Base documentation;
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for more general information on REST web services, see the article here[http://en.wikipedia.org/wiki/Representational_State_Transfer].
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GET Http requests expect the XML form of whatever resource/resources is/are being requested. So,
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for a request for a single element - the XML of that item is expected in response:
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# Expects a response of
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# <person><id type="integer">1</id><attribute1>value1</attribute1><attribute2>..</attribute2></person>
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# for GET http://api.people.com:3000/people/1.xml
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The XML document that is received is used to build a new object of type Person, with each
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XML element becoming an attribute on the object.
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ryan.is_a? Person #=> true
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ryan.attribute1 #=> 'value1'
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Any complex element (one that contains other elements) becomes its own object:
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# <person><id>1</id><attribute1>value1</attribute1><complex><attribute2>value2</attribute2></complex></person>
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# for GET http://api.people.com:3000/people/1.xml
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ryan.complex #=> <Person::Complex::xxxxx>
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ryan.complex.attribute2 #=> 'value2'
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Collections can also be requested in a similar fashion
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# Expects a response of
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# <people type="array">
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# <person><id type="integer">1</id><first>Ryan</first></person>
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# <person><id type="integer">2</id><first>Jim</first></person>
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# for GET http://api.people.com:3000/people.xml
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people = Person.find(:all)
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people.first #=> <Person::xxx 'first' => 'Ryan' ...>
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people.last #=> <Person::xxx 'first' => 'Jim' ...>
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Creating a new resource submits the xml form of the resource as the body of the request and expects
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a 'Location' header in the response with the RESTful URL location of the newly created resource. The
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id of the newly created resource is parsed out of the Location response header and automatically set
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as the id of the ARes object.
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# <person><first>Ryan</first></person>
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# is submitted as the body on
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# POST http://api.people.com:3000/people.xml
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# when save is called on a new Person object. An empty response is
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# is expected with a 'Location' header value:
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# Response (201): Location: http://api.people.com:3000/people/2
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ryan = Person.new(:first => 'Ryan')
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'save' is also used to update an existing resource - and follows the same protocol as creating a resource
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with the exception that no response headers are needed - just an empty response when the update on the
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server side was successful.
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# <person><first>Ryan</first></person>
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# is submitted as the body on
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# PUT http://api.people.com:3000/people/1.xml
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# when save is called on an existing Person object. An empty response is
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# is expected with code (204)
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ryan = Person.find(1)
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ryan.first #=> 'Ryan'
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ryan.first = 'Rizzle'
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Destruction of a resource can be invoked as a class and instance method of the resource.
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# A request is made to
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# DELETE http://api.people.com:3000/people/1.xml
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# for both of these forms. An empty response with
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# is expected with response code (200)
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ryan = Person.find(1)
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ryan.destroy #=> true
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ryan.exists? #=> false
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Person.delete(2) #=> true
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Person.exists?(2) #=> false
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You can find more usage information in the ActiveResource::Base documentation.