Grape::Roar

Use Roar with Grape.

Table of Contents

• Demo
• Installation
• Usage
  • Tell your API to use Grape::Formatter::Roar
  • Use Grape’s Present
  • Accessing the Request Inside a Representer
  • Decorators
  • Relation Extensions
    • Designing Representers
      • Example Models
      • Example Representers
      • Example Item
      • Example Cart
    • Errors
    • Change how URLs are presented
      • Override base URI mappings
      • Override resource URI mappings
    • Designing Adapters
      • Example: ActiveRecord Adapter
      • Validations
• Contributing
• Copyright and License

Demo

See grape-with-roar.

Installation

Add the grape, roar and grape-roar gems to Gemfile.

gem 'grape'
gem 'roar'
gem 'grape-roar'

If you're upgrading from an older version of this gem, please see UPGRADING.

Usage

Tell your API to use Grape::Formatter::Roar

class API < Grape::API
  format :json
  formatter :json, Grape::Formatter::Roar
end

Use Grape's Present

Include Grape::Roar::Representer into a representer module after any Roar mixins, then use Grape's present keyword.

module ProductRepresenter
  include Roar::JSON
  include Roar::Hypermedia
  include Grape::Roar::Representer

  property :title
  property :id
end

get 'product/:id' do
  present Product.find(params[:id]), with: ProductRepresenter
end

Presenting collections works the same way. The following example returns an embedded set of products in the HAL Hypermedia format.

module ProductsRepresenter
  include Roar::JSON::HAL
  include Roar::Hypermedia
  include Grape::Roar::Representer

  collection :entries, extend: ProductRepresenter, as: :products, embedded: true
end

get 'products' do
  present Product.all, with: ProductsRepresenter
end

Accessing the Request Inside a Representer

The formatter invokes to_json on presented objects and provides access to the requesting environment via the env option. The following example renders a full request URL in a representer.

module ProductRepresenter
  include Roar::JSON
  include Roar::Hypermedia
  include Grape::Roar::Representer

  link :self do |opts|
    request = Grape::Request.new(opts[:env])
    "#{request.url}"
  end
end

Decorators

If you prefer to use a decorator class instead of modules.

class ProductRepresenter < Grape::Roar::Decorator
  include Roar::JSON
  include Roar::Hypermedia

  link :self do |opts|
    "#{request(opts).url}/#{represented.id}"
  end

  private

  def request(opts)
    Grape::Request.new(opts[:env])
  end
end

get 'products' do
  present Product.all, with: ProductsRepresenter
end

Relation Extensions

If you use either ActiveRecord or Mongoid, you can use the Grape::Roar::Extensions::Relations DSL to expose the relationships in between your models as a HAL response. The DSL methods used are the same regardless of what your ORM/ODM is, as long as there exists an adapter for it.

Designing Representers

Arguments passed to #relation are forwarded to roar. Single member relations (e.g. belongs_to) are represented using #property, collections are represented using #collection; arguments provided to #relation will be passed through these methods (i.e. additional arguments roar and representable accept).

A default base URI is constructed from a Grape::Request by concatenating the #base_url and #script_name properties. The resource path is extracted from the name of the relation.

Otherwise, the extensions attempt to look up the correct representer module/class for the objects (e.g. we infer the extend argument). You can always specify the correct representer to use on your own.

Example Models

class Item < ActiveRecord::Base
  belongs_to :cart
end

class Cart < ActiveRecord::Base
  has_many :items  
end

Example Representers

class ItemEntity < Grape::Roar::Decorator
  include Roar::JSON
  include Roar::JSON::HAL
  include Roar::Hypermedia

  include Grape::Roar::Extensions::Relations

  # Cart will be presented under the _embedded key
  relation :belongs_to, :cart, embedded: true

  link_self
end

class CartEntity < Grape::Roar::Decorator
  include Roar::JSON
  include Roar::JSON::HAL
  include Roar::Hypermedia

  include Grape::Roar::Extensions::Relations

  # Items will be presented under the _links key
  relation :has_many, :items, embedded: false

  link_self
end

Although this example uses Grape::Roar::Decorator, you can also use a module as show in prior examples above. If doing so, you no longer have to mix in Grape::Roar::Representer.

Example Item

{
    "_embedded": {
        "cart": {
            "_links": {
                "self": {
                    "href": "http://example.org/carts/1"
                },
                "items": [{
                    "href": "http://example.org/items/1"
                }]
            }
        }
    },
    "_links": {
        "self": {
            "href": "http://example.org/items/1"
        }
    }
}

Example Cart

{
    "_links": {
        "self": {
            "href": "http://example.org/carts/1"
        },
        "items": [{
            "href": "http://example.org/items/1"
        }, {
            "href": "http://example.org/items/2"
        }, {
            "href": "http://example.org/items/3"
        }, {
            "href": "http://example.org/items/4"
        }, {
            "href": "http://example.org/items/5"
        }]
    }
}

Errors

Should you incorrectly describe a relationship (e.g. you specify has_one but your model specifies has_many), an exception will be raised to notify you of the mismatch:

Grape::Roar::Extensions::Relations::Exceptions::InvalidRelationError:
  Expected Mongoid::Association::Referenced::HasOne, got Mongoid::Association::Referenced::HasMany!

Change how URLs are presented

The opts hash below is the same one as shown in prior examples.

Override base URI mappings

class BarEntity < Grape::Roar::Decorator
  include Roar::JSON
  include Roar::JSON::HAL
  include Roar::Hypermedia

  include Grape::Roar::Extensions::Relations

  # This is our default implementation
  map_base_url do |opts|
    request = Grape::Request.new(opts[:env])
    "#{request.base_url}#{request.script_name}"
  end

  relation :has_many, :bars, embedded: false
end

Override resource URI mappings

class BarEntity < Grape::Roar::Decorator
  include Roar::JSON
  include Roar::JSON::HAL
  include Roar::Hypermedia

  include Grape::Roar::Extensions::Relations

  # This is our default implementation
  map_resource_path do |_opts, object, relation_name|
    "#{relation_name}/#{object.id}"
  end

  relation :has_many, :bars, embedded: false
end

Designing Adapters

If you have custom domain objects, you can create an adapter to make your models compatible with the DSL methods. Below is an example of the ActiveRecord adapter.

Example: ActiveRecord Adapter

module Extensions
  module RelationalModels
    module Adapter
      class ActiveRecord < Base
        include Validations::ActiveRecord

        # We map your domain object to the correct adapter
        # at runtime.
        valid_for { |klass| klass < ::ActiveRecord::Base }

        def collection_methods
          @collection_methods ||= %i(has_many has_and_belongs_to_many)
        end

        def name_for_represented(represented)
          klass_name = case represented
                       when ::ActiveRecord::Relation
                         represented.klass.name
                       else
                         represented.class.name
                       end
          klass_name.demodulize.pluralize.downcase
        end

        def single_entity_methods
          @single_entity_methods ||= %i(has_one belongs_to)
        end
      end
    end
  end
end

Validations

Errors are handled by creating methods corresponding to those in collection_methods and single_entity_methods. For example, this is the validator for belongs_to:

module ActiveRecord
  include Validations::Misc

  def belongs_to_valid?(relation)
    relation = klass.reflections[relation]

    return true if relation.is_a?(
      ::ActiveRecord::Reflection::BelongsToReflection
    )

    # Provided by Validations::Misc
    invalid_relation(
      ::ActiveRecord::Reflection::BelongsToReflection,
      relation.class
    )
  end
end

After writing your validation methods, just mix them into your adapter. You can choose to not write validation methods; they are only invoked if your adapter responds to them.

Contributing

See CONTRIBUTING.

Copyright and License

MIT License, see LICENSE for details.

(c) 2012-2025 Daniel Doubrovkine & Contributors, Artsy