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A Ruby implementation of Apollo Federation
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apollo-federation

This gem extends the GraphQL Ruby gem to add support for creating an Apollo Federation schema.

DISCLAIMER

This gem is still in a beta stage and may have some bugs or incompatibilities. See the Known Issues and Limitations below. If you run into any problems, please file an issue.

Installation

Add this line to your application's Gemfile:

gem 'apollo-federation'

And then execute:

$ bundle

Or install it yourself as:

$ gem install apollo-federation

Getting Started

Include the ApolloFederation::Field module in your base field class:

require 'apollo-federation'

class BaseField < GraphQL::Schema::Field
  include ApolloFederation::Field
end

Include the ApolloFederation::Object module in your base object class:

class BaseObject < GraphQL::Schema::Object
  include ApolloFederation::Object

  field_class BaseField
end

Include the ApolloFederation::Interface module in your base interface module:

module BaseInterface
  include GraphQL::Schema::Interface
  include ApolloFederation::Interface

  field_class BaseField
end

Finally, include the ApolloFederation::Schema module in your schema:

class MySchema < GraphQL::Schema
  include ApolloFederation::Schema
end

Example

The example folder contains a Ruby implementation of Apollo's federation-demo. To run it locally, install the Ruby dependencies:

$ bundle

Install the Node dependencies:

$ yarn

Start all of the services:

$ yarn start-services

Start the gateway:

$ yarn start-gateway

This will start up the gateway and serve it at http://localhost:5000.

Usage

The API is designed to mimic the API of Apollo's federation library. It's best to read and understand the way federation works, in general, before attempting to use this library.

Extending a type

Apollo documentation

Call extend_type within your class definition:

class User < BaseObject
  extend_type
end

The @key directive

Apollo documentation

Call key within your class definition:

class User < BaseObject
  key fields: 'id'
end

The @external directive

Apollo documentation

Pass the external: true option to your field definition:

class User < BaseObject
  field :id, ID, null: false, external: true
end

The @requires directive

Apollo documentation

Pass the requires: option to your field definition:

class Product < BaseObject
  field :price, Int, null: true, external: true
  field :weight, Int, null: true, external: true
  field :shipping_estimate, Int, null: true, requires: { fields: "price weight"}
end

The @provides directive

Apollo documentation

Pass the provides: option to your field definition:

class Review < BaseObject
  field :author, 'User', null: true, provides: { fields: 'username' }
end

Reference resolvers

Apollo documentation

Define a resolve_reference class method on your object. The method will be passed the reference from another service and the context for the query.

class User < BaseObject
  def self.resolve_reference(reference, context)
    USERS.find { |user| user[:id] == reference[:id] }
  end
end

Tracing

To support federated tracing:

  1. Add use ApolloFederation::Tracing to your schema class.
  2. Change your controller to add tracing_enabled: true to the execution context based on the presence of the "include trace" header:
    def execute
      # ...
      context = {
        tracing_enabled: ApolloFederation::Tracing.should_add_traces(headers)
      }
      # ...
    end
  3. Change your controller to attach the traces to the response:
    def execute
      # ...
      result = YourSchema.execute(query, ...)
      render json: ApolloFederation::Tracing.attach_trace_to_result(result)
    end

Known Issues and Limitations

  • Only works with class-based schemas, the legacy .define API will not be supported
  • Does not add directives to the output of Schema.to_definition. Since graphql-ruby doesn't natively support schema directives, the directives will only be visible to the Apollo Gateway through the Query._service field (see the Apollo Federation specification)

Maintainers

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