Grape::Entity

Introduction

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

Example

module API
  module Entities
    class User < Grape::Entity
      expose :id, :name, :email
    end
    
    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 status.txt
      end
      expose :replies, using: API::Entities::Status, as: :replies
      expose :last_reply, using: API::Entities::Status do |status, options|
        status.replies.last
      end

      with_options(format_with: :iso_timestamp) do
        expose :created_at
        expose :updated_at
      end
      
      # Expose User if the Status is not being flattened.
      expose :user, using: API::Entities::User, unless: { flatten: true }
      
      # "Flatten" User exposures into the Status entity.
      # This will add :user_name and :user_email to the status (skipping :id).
      merge_with API::Entities::User, prefix: "user_", except: :id, if: { flatten: true } do
        object.user
      end
    end
  end
end

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

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.

Basic Exposure

Define a list of fields that will always be exposed.

expose :user_name, :ip

Exposing with a Presenter

Don't derive your model classes from Grape::Entity, expose them using a presenter.

expose :replies, using: API::Entities::Status, as: :replies

Conditional Exposure

Use :if or :unless to expose fields conditionally.

expose :ip, if: { type: :full }

expose :ip, if: lambda { |instance, options| options[:type] == :full } # exposed if the function evaluates to true
expose :ip, if: :type # exposed if :type is available in the options hash
expose :ip, if { type: :full } # exposed if options :type has a value of :full

expose :ip, unless: ... # the opposite of :if

Safe Exposure

Don't raise an exception and expose as nil, even if the :x cannot be evaluated.

expose :ip, safe: true

Runtime Exposure

Use a block or a Proc to evaluate exposure at runtime.

expose :digest do |status, options|
  Digest::MD5.hexdigest status.txt
end

expose :digest, proc: ... # equivalent to a block

You can also define a method on the entity and it will try that before trying on the object the entity wraps.

class ExampleEntity < Grape::Entity
  expose :attr_not_on_wrapped_object
  # ...
private

  def attr_not_on_wrapped_object
    42
  end
end

Aliases

Expose under a different name with :as.

expose :replies, using: API::Entities::Status, as: :replies

Format Before Exposing

Apply a formatter before exposing a value.

format_with(:iso_timestamp) { |dt| dt.iso8601 }
with_options(format_with: :iso_timestamp) do
  expose :created_at
  expose :updated_at
end

Documentation

Expose documentation with the field. Gets bubbled up when used with Grape and various API documentation systems.

expose :text, documentation: { type: "String", desc: "Status update text." }

Options Hash

The option keys :version and :collection are always 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. The options also contain the runtime environment in :env, which includes request parameters in options[:env][:grape.request.params].

Any additional options defined on the entity exposure are included as is. In the following example user is set to the value of current_user.

class Status < Grape::Entity
  expose :user, if: lambda { |instance, options| options[:user] } do |instance, options|
    # examine available environment keys with `p options[:env].keys`
    options[:user]
  end
end

present s, with: Status, user: current_user

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

With Grape, 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.', {
      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
    Entity.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

Testing with Entities

Test API request/response as usual.

Also see Grape Entity Matchers.

Project Resources

• Need help? Grape Google Group

Contributing

1. Fork the project
2. Create your feature branch (git checkout -b my-new-feature)
3. Write tests. Make changes. Run rubocop.
4. Commit your changes (git commit -am 'Add some feature')
5. Push to the branch (git push origin my-new-feature)
6. Create a new pull request

License

MIT License. See LICENSE for details.

Copyright

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