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120 lines
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120 lines
4 KiB
Text
h2. Active Resource Basics
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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.
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endprologue.
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WARNING. This Guide is based on Rails 3.0. Some of the code shown here will not work in earlier versions of Rails.
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h3. Introduction
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Active Resource allows you to connect with RESTful web services. So, in Rails, Resource classes inherited from +ActiveResource::Base+ and live in +app/models+.
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h3. Configuration and Usage
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Putting Active Resource to use is very similar to Active Record. 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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<ruby>
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class Person < ActiveResource::Base
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self.site = "http://api.people.com:3000/"
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end
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</ruby>
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Now the Person class is REST enabled and can invoke REST services very similarly to how Active Record invokes
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life cycle methods that operate against a persistent store.
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h3. Reading and Writing Data
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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.
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h4. Read
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Read requests use the GET method and expect the JSON form of whatever resource/resources is/are being requested.
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<ruby>
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# Find a person with id = 1
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person = Person.find(1)
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# Check if a person exists with id = 1
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Person.exists?(1) # => true
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# Get all resources of Person class
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Person.all
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</ruby>
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h4. Create
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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.
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<ruby>
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person = Person.create(:name => 'Vishnu')
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person.id # => 1
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</ruby>
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h4. Update
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To update an existing resource, 'save' method is used. This method make a HTTP PUT request in JSON format.
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<ruby>
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person = Person.find(1)
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person.name = 'Atrai'
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person.save
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</ruby>
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h4. Delete
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'destroy' method makes a HTTP DELETE request for an existing resource in JSON format to delete that resource.
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<ruby>
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person = Person.find(1)
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person.destroy
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</ruby>
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h3. Validations
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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.
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h4. Validating client side resources by overriding validation methods in base class
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<ruby>
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class Person < ActiveResource::Base
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self.site = "http://api.people.com:3000/"
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protected
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def validate
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errors.add("last", "has invalid characters") unless last =~ /[a-zA-Z]*/
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end
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end
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</ruby>
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h4. Validating client side resources
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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:
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<ruby>
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person = Person.new(:first_name => "Jim", :last_name => "")
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person.save # => false (server returns an HTTP 422 status code and errors)
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person.valid? # => false
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person.errors.empty? # => false
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person.errors.count # => 1
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person.errors.full_messages # => ["Last name can't be empty"]
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person.errors[:last_name] # => ["can't be empty"]
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person.last_name = "Halpert"
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person.save # => true (and person is now saved to the remote service)
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</ruby>
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h4. Public instance methods
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ActiveResource::Validations have three public instance methods
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h5. errors()
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This will return errors object that holds all information about attribute error messages
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h5. save_with_validation(options=nil)
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This validates the resource with any local validations written in base class and then it will try to POST if there are no errors.
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h5. valid?
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Runs all the local validations and will return true if no errors.
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