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 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, | status.user.public? }
expose :contact_info do
expose :phone
expose :address, using: API::Address
end
expose :digest do |status, |
Digest::MD5.hexdigest status.txt
end
expose :replies, using: API::Status, as: :replies
expose :last_reply, using: API::Status do |status, |
status.replies.last
end
(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
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::Status, as: :replies
Presenter classes can also be specified in string format, which helps with circular dependencies.
expose :replies, using: `API::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
Nested Exposure
Supply a block to define a hash using nested exposures.
expose :contact_info do
expose :phone
expose :address, using: API::Address
end
Collection Exposure
Use root(plural, singular = nil)
to expose an object or a collection of objects with a root key.
root 'users', 'user'
expose :id, :name, ...
Runtime Exposure
Use a block or a Proc
to evaluate exposure at runtime. The supplied block or
Proc
will be called with two parameters: the represented object and runtime options.
NOTE: A block supplied with no parameters will be evaluated as a nested exposure (see above).
expose :digest do |status, |
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::Status, as: :replies
Format Before Exposing
Apply a formatter before exposing a value.
format_with(:iso_timestamp) { |dt| dt.iso8601 }
(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, | [:user] } do |instance, |
# examine available environment keys with `p options[:env].keys`
[: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.', {
params: 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, | object.check == "foo" }
expose :field_b, :foo, if: lambda { |object, | 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, | object.check == "foo" }
expose :field_b, if: lambda { |object, | object.check == "bar" }
expose :foo, if: lambda { |object, | object.respond_to?(:foo) }
end
end
end
Also note that an ArgumentError
is raised when unknown options are passed to either expose
or with_options
.
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
- Fork the project
- Create your feature branch (
git checkout -b my-new-feature
) - Write tests. Make changes. Run
rubocop
. - Commit your changes (
git commit -am 'Add some feature'
) - Push to the branch (
git push origin my-new-feature
) - Create a new pull request
License
MIT License. See LICENSE for details.
Copyright
Copyright (c) 2010-2013 Michael Bleigh, Intridea, Inc., and contributors.