ActiveResource::Base

ActiveResource::Base is the main class for mapping RESTful resources as models in a Rails application.

For an outline of what Active Resource is capable of, see its README.

Automated mapping

Active Resource objects represent your RESTful resources as manipulatable Ruby objects. To map resources to Ruby objects, Active Resource only needs a class name that corresponds to the resource name (e.g., the class Person maps to the resources people, very similarly to Active Record) and a site value, which holds the URI of the resources.

  class Person < ActiveResource::Base
    self.site = "http://api.people.com:3000/"
  end

Now the Person class is mapped to RESTful resources located at api.people.com:3000/people/, and you can now use Active Resource’s life cycle methods to manipulate resources. In the case where you already have an existing model with the same name as the desired RESTful resource you can set the element_name value.

  class PersonResource < ActiveResource::Base
    self.site = "http://api.people.com:3000/"
    self.element_name = "person"
  end

If your Active Resource object is required to use an HTTP proxy you can set the proxy value which holds a URI.

  class PersonResource < ActiveResource::Base
    self.site = "http://api.people.com:3000/"
    self.proxy = "http://user:password@proxy.people.com:8080"
  end

Life cycle methods

Active Resource exposes methods for creating, finding, updating, and deleting resources from REST web services.

  ryan = Person.new(:first => 'Ryan', :last => 'Daigle')
  ryan.save                # => true
  ryan.id                  # => 2
  Person.exists?(ryan.id)  # => true
  ryan.exists?             # => true

  ryan = Person.find(1)
  # Resource holding our newly created Person object

  ryan.first = 'Rizzle'
  ryan.save                # => true

  ryan.destroy             # => true

As you can see, these are very similar to Active Record’s life cycle methods for database records. You can read more about each of these methods in their respective documentation.

Custom REST methods

Since simple CRUD/life cycle methods can’t accomplish every task, Active Resource also supports defining your own custom REST methods. To invoke them, Active Resource provides the get, post, put and delete methods where you can specify a custom REST method name to invoke.

  # POST to the custom 'register' REST method, i.e. POST /people/new/register.json.
  Person.new(:name => 'Ryan').post(:register)
  # => { :id => 1, :name => 'Ryan', :position => 'Clerk' }

  # PUT an update by invoking the 'promote' REST method, i.e. PUT /people/1/promote.json?position=Manager.
  Person.find(1).put(:promote, :position => 'Manager')
  # => { :id => 1, :name => 'Ryan', :position => 'Manager' }

  # GET all the positions available, i.e. GET /people/positions.json.
  Person.get(:positions)
  # => [{:name => 'Manager'}, {:name => 'Clerk'}]

  # DELETE to 'fire' a person, i.e. DELETE /people/1/fire.json.
  Person.find(1).delete(:fire)

For more information on using custom REST methods, see the ActiveResource::CustomMethods documentation.

Validations

You can validate resources client side by overriding validation methods in the base class.

  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

See the ActiveResource::Validations documentation for more information.

Authentication

Many REST APIs will require authentication, usually in the form of basic HTTP authentication. Authentication can be specified by:

HTTP Basic Authentication

putting the credentials in the URL for the site variable.

 class Person < ActiveResource::Base
   self.site = "http://ryan:password@api.people.com:3000/"
 end

defining user and/or password variables

 class Person < ActiveResource::Base
   self.site = "http://api.people.com:3000/"
   self.user = "ryan"
   self.password = "password"
 end

For obvious security reasons, it is probably best if such services are available over HTTPS.

Note: Some values cannot be provided in the URL passed to site. e.g. email addresses as usernames. In those situations you should use the separate user and password option.

Certificate Authentication

End point uses an X509 certificate for authentication. See ssl_options= for all options.

 class Person < ActiveResource::Base
   self.site = "https://secure.api.people.com/"
   self.ssl_options = {:cert         => OpenSSL::X509::Certificate.new(File.open(pem_file))
                       :key          => OpenSSL::PKey::RSA.new(File.open(pem_file)),
                       :ca_path      => "/path/to/OpenSSL/formatted/CA_Certs",
                       :verify_mode  => OpenSSL::SSL::VERIFY_PEER}
 end

Errors & Validation

Error handling and validation is handled in much the same manner as you’re used to seeing in Active Record. Both the response code in the HTTP response and the body of the response are used to indicate that an error occurred.

Resource errors

When a GET is requested for a resource that does not exist, the HTTP 404 (Resource Not Found) response code will be returned from the server which will raise an ActiveResource::ResourceNotFound exception.

  # GET http://api.people.com:3000/people/999.json
  ryan = Person.find(999) # 404, raises ActiveResource::ResourceNotFound

404 is just one of the HTTP error response codes that Active Resource will handle with its own exception. The following HTTP response codes will also result in these exceptions:

200..399 - Valid response. No exceptions, other than these redirects:
301, 302, 303, 307 - ActiveResource::Redirection
400 - ActiveResource::BadRequest
401 - ActiveResource::UnauthorizedAccess
403 - ActiveResource::ForbiddenAccess
404 - ActiveResource::ResourceNotFound
405 - ActiveResource::MethodNotAllowed
409 - ActiveResource::ResourceConflict
410 - ActiveResource::ResourceGone
422 - ActiveResource::ResourceInvalid (rescued by save as validation errors)
401..499 - ActiveResource::ClientError
500..599 - ActiveResource::ServerError
Other - ActiveResource::ConnectionError

These custom exceptions allow you to deal with resource errors more naturally and with more precision rather than returning a general HTTP error. For example:

  begin
    ryan = Person.find(my_id)
  rescue ActiveResource::ResourceNotFound
    redirect_to :action => 'not_found'
  rescue ActiveResource::ResourceConflict, ActiveResource::ResourceInvalid
    redirect_to :action => 'new'
  end

When a GET is requested for a nested resource and you don’t provide the prefix_param an ActiveResource::MissingPrefixParam will be raised.

 class Comment < ActiveResource::Base
   self.site = "http://someip.com/posts/:post_id/"
 end

 Comment.find(1)
 # => ActiveResource::MissingPrefixParam: post_id prefix_option is missing

Validation errors

Active Resource supports validations on resources and will return errors if any of these validations fail (e.g., “First name can not be blank” and so on). These types of errors are denoted in the response by a response code of 422 and an XML or JSON representation of the validation errors. The save operation will then fail (with a false return value) and the validation errors can be accessed on the resource in question.

  ryan = Person.find(1)
  ryan.first # => ''
  ryan.save  # => false

  # When
  # PUT http://api.people.com:3000/people/1.json
  # or
  # PUT http://api.people.com:3000/people/1.json
  # is requested with invalid values, the response is:
  #
  # Response (422):
  # <errors><error>First cannot be empty</error></errors>
  # or
  # {"errors":["First cannot be empty"]}
  #

  ryan.errors.invalid?(:first)  # => true
  ryan.errors.full_messages     # => ['First cannot be empty']

Learn more about Active Resource’s validation features in the ActiveResource::Validations documentation.

Timeouts

Active Resource relies on HTTP to access RESTful APIs and as such is inherently susceptible to slow or unresponsive servers. In such cases, your Active Resource method calls could timeout. You can control the amount of time before Active Resource times out with the timeout variable.

  class Person < ActiveResource::Base
    self.site = "http://api.people.com:3000/"
    self.timeout = 5
  end

This sets the timeout to 5 seconds. You can adjust the timeout to a value suitable for the RESTful API you are accessing. It is recommended to set this to a reasonably low value to allow your Active Resource clients (especially if you are using Active Resource in a Rails application) to fail-fast (see en.wikipedia.org/wiki/Fail-fast) rather than cause cascading failures that could incapacitate your server.

When a timeout occurs, an ActiveResource::TimeoutError is raised. You should rescue from ActiveResource::TimeoutError in your Active Resource method calls.

Internally, Active Resource relies on Ruby’s Net::HTTP library to make HTTP requests. Setting timeout sets the read_timeout of the internal Net::HTTP instance to the same value. The default read_timeout is 60 seconds on most Ruby implementations.

Methods

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