Add field mixin to type configurations ?

lib/graphql.rb

@@ -44,6 +44,7 @@ def self.parse_with_parslet(string)
 require 'graphql/enum_type'
 require 'graphql/input_object_type'
 require 'graphql/interface_type'
+require 'graphql/mixin'
 require 'graphql/list_type'
 require 'graphql/non_null_type'
 require 'graphql/union_type'

lib/graphql/definition_helpers/defined_by_config.rb

@@ -52,6 +52,10 @@ def types
       GraphQL::DefinitionHelpers::TypeDefiner.instance
     end
 
+    def mixin(mixin)
+      @fields = mixin.fields.merge(@fields)
+    end
+
     def field(name, type = nil, desc = nil, field: nil, property: nil, &block)
       if block_given?
         field = GraphQL::Field.define(&block)

lib/graphql/mixin.rb

@@ -0,0 +1,7 @@
+module GraphQL
+  class Mixin
+    include GraphQL::DefinitionHelpers::DefinedByConfig
+    defined_by_config :fields
+    attr_accessor :fields
+  end
+end

spec/graphql/introspection/type_type_spec.rb

@@ -12,6 +12,8 @@
   |}
   let(:result) { DummySchema.execute(query_string, context: {}, variables: {"cheeseId" => 2}) }
   let(:cheese_fields) {[
+    {"name"=>"cents",       "isDeprecated" => false, "type" => { "name" => "Non-Null", "ofType" => { "name" => "Int"}}},
+    {"name"=>"currency",    "isDeprecated" => false, "type" => { "name" => "Non-Null", "ofType" => { "name" => "String"}}},
     {"name"=>"id",          "isDeprecated" => false, "type" => { "name" => "Non-Null", "ofType" => { "name" => "Int"}}},
     {"name"=>"flavor",      "isDeprecated" => false, "type" => { "name" => "Non-Null", "ofType" => { "name" => "String"}}},
     {"name"=>"origin",      "isDeprecated" => false, "type" => { "name" => "Non-Null", "ofType" => { "name" => "String"}}},
@@ -37,7 +39,9 @@
           {"name"=>"AnimalProduct"}
         ],
         "fields"=>[
-          {"type"=>{"name"=>"Non-Null", "ofType"=>{"name"=>"ID"}}},
+          {"type"=>{"name"=>"Non-Null","ofType"=>{"name"=>"Int"}}},
+          {"type"=>{"name"=>"Non-Null","ofType"=>{"name"=>"String"}}},
+          {"type"=>{"name"=>"Non-Null","ofType"=>{"name"=>"ID"}}},
           {"type"=>{"name"=>"DairyAnimal", "ofType"=>nil}},
           {"type"=>{"name"=>"Non-Null", "ofType"=>{"name"=>"String"}}},
           {"type"=>{"name"=>"Non-Null", "ofType"=>{"name"=>"Float"}}},

spec/support/dairy_app.rb

@@ -24,11 +24,16 @@ class NoSuchDairyError < StandardError; end
   value("YAK",    "Animal with long hair", deprecation_reason: "Out of fashion")
 end
 
+HasPrice = GraphQL::Mixin.define do
+  field :cents, !types.Int 
+  field :currency, !types.String
+end
+
 CheeseType = GraphQL::ObjectType.define do
   name "Cheese"
   description "Cultured dairy product"
   interfaces [EdibleInterface, AnimalProductInterface]
-
+  mixin HasPrice
   # Can have (name, type, desc)
   field :id, !types.Int, "Unique identifier"
   field :flavor, !types.String, "Kind of Cheese"
@@ -62,6 +67,7 @@ class NoSuchDairyError < StandardError; end
   name 'Milk'
   description "Dairy beverage"
   interfaces [EdibleInterface, AnimalProductInterface]
+  mixin HasPrice
   field :id, !types.ID
   field :source, DairyAnimalEnum, "Animal which produced this milk"
   field :origin, !types.String, "Place the milk comes from"