Entities - a simple Facade to use with your models and API - extracted from Grape.
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README.markdown

Grape::Entity

Build Status

Introduction

This gem adds Entity support to API frameworks, such as Grape. Grape's Entity is an API focussed facade that sits on top of an object model.

What's New

We are currently working on a set of "shoulda-style matchers" (sorry, RSpec only right now -- although they've been done in a way that can support test-unit in the future).

Grape Entity Matchers.

This is still a work in progress but worth checking out.

Reusable Responses with Entities

Entities are a reusable means for converting Ruby objects to API responses. Entities can be used to conditionally include fields, nest other entities, and build ever larger responses, using inheritance.

Defining Entities

Entities inherit from Grape::Entity, and define a simple DSL. Exposures can use runtime options to determine which fields should be visible, these options are available to :if, :unless, and :proc. The option keys :version and :collection will always be defined. The :version key is defined as api.version. The :collection key is boolean, and defined as true if the object presented is an array.

  • expose SYMBOLS
    • define a list of fields which will always be exposed
  • expose SYMBOLS, HASH
    • HASH keys include :if, :unless, :proc, :as, :using, :format_with, :documentation
      • :if and :unless accept hashes (passed during runtime), procs (arguments are object and options), or symbols (checks for presence of the specified key on the options hash)
  • expose SYMBOL, { :format_with => :formatter }
    • expose a value, formatting it first
    • :format_with can only be applied to one exposure at a time
  • expose SYMBOL, { :as => "alias" }
    • Expose a value, changing its hash key from SYMBOL to alias
    • :as can only be applied to one exposure at a time
  • expose SYMBOL BLOCK
    • block arguments are object and options
    • expose the value returned by the block
    • block can only be applied to one exposure at a time
  • with_options HASH BLOCK
    • exposures defined within a with_options block will inherit any options defined in HASH. Same keys available as expose SYMBOLS, HASH
module API
  module Entities
    class Status < Grape::Entity
      format_with :iso_timestamp { |dt| dt.iso8601 }
        
      expose :user_name
      expose :text, :documentation => { :type => "string", :desc => "Status update text." }
      expose :ip, :if => { :type => :full }
      expose :user_type, :user_id, :if => lambda{ |status, options| status.user.public? }
      expose :digest do
        |status, options| Digest::MD5.hexdigest(satus.txt)
      end
      expose :replies, :using => API::Status, :as => :replies

      with_options { :format_with => :iso_timestamp } do
        expose :created_at
        expose :updated_at
      end
    end
  end
end

module API
  module Entities
    class StatusDetailed < API::Entities::Status
      expose :internal_id
    end
  end
end

Using the Exposure DSL

Grape ships with a DSL to easily define entities within the context of an existing class:

class Status
  include Grape::Entity::DSL

  entity :text, :user_id do
    expose :detailed, if: :conditional
  end
end

The above will automatically create a Status::Entity class and define properties on it according to the same rules as above. If you only want to define simple exposures you don't have to supply a block and can instead simply supply a list of comma-separated symbols.

Using Entities

Once an entity is defined, it can be used within endpoints, by calling present. The present method accepts two arguments, the object to be presented and the options associated with it. The options hash must always include :with, which defines the entity to expose.

If the entity includes documentation it can be included in an endpoint's description.

module API
  class Statuses < Grape::API
    version 'v1'

    desc 'Statuses index', {
      :object_fields => API::Entities::Status.documentation
    }
    get '/statuses' do
      statuses = Status.all
      type = current_user.admin? ? :full : :default
      present statuses, with: API::Entities::Status, :type => type
    end
  end
end

Entity Organization

In addition to separately organizing entities, it may be useful to put them as namespaced classes underneath the model they represent.

class Status
  def entity
    Status.new(self)
  end

  class Entity < Grape::Entity
    expose :text, :user_id
  end
end

If you organize your entities this way, Grape will automatically detect the Entity class and use it to present your models. In this example, if you added present User.new to your endpoint, Grape would automatically detect that there is a Status::Entity class and use that as the representative entity. This can still be overridden by using the :with option or an explicit represents call.

Caveats

Entities with duplicate exposure names and conditions will silently overwrite one another. In the following example, when object.check equals "foo", only field_a will be exposed. However, when object.check equals "bar" both field_b and foo will be exposed.

module API
  module Entities
    class Status < Grape::Entity
      expose :field_a, :foo, :if => lambda { |object, options| object.check == "foo" }
      expose :field_b, :foo, :if => lambda { |object, options| object.check == "bar" }
    end
  end
end

This can be problematic, when you have mixed collections. Using respond_to? is safer.

module API
  module Entities
    class Status < Grape::Entity
      expose :field_a, :if => lambda { |object, options| object.check == "foo" }
      expose :field_b, :if => lambda { |object, options| object.check == "bar" }
      expose :foo, :if => lambda { |object, options| object.respond_to?(:foo) }
    end
  end
end

Installation

Add this line to your application's Gemfile:

gem 'grape-entity'

And then execute:

$ bundle

Or install it yourself as:

$ gem install grape-entity

Contributing

  1. Fork it
  2. Create your feature branch (git checkout -b my-new-feature)
  3. Commit your changes (git commit -am 'Add some feature')
  4. Push to the branch (git push origin my-new-feature)
  5. Create new Pull Request

License

MIT License. See LICENSE for details.

Copyright

Copyright (c) 2010-2013 Michael Bleigh, and Intridea, Inc.