Add GraphQL query & type

Author: tsugitta

app/graphql/sources/posts_by_user.rb

@@ -0,0 +1,10 @@
+# frozen_string_literal: true
+
+module Sources
+  class PostsByUser < GraphQL::Dataloader::Source
+    def fetch(user_ids)
+      posts = Post.where(user_id: user_ids).group_by(&:user_id)
+      user_ids.map { |uid| posts[uid] || [] }
+    end
+  end
+end

app/graphql/types/post_type.rb

@@ -0,0 +1,8 @@
+# frozen_string_literal: true
+
+module Types
+  class PostType < Types::BaseObject
+    field :id, ID, null: false
+    field :title, String
+  end
+end

app/graphql/types/query_type.rb

@@ -27,5 +27,10 @@ def nodes(ids:)
     def test_field
       "Hello World!"
     end
+
+    field :users, [Types::UserType], null: false
+    def users
+      User.all
+    end
   end
 end

app/graphql/types/user_type.rb

@@ -0,0 +1,21 @@
+# frozen_string_literal: true
+
+module Types
+  class UserType < Types::BaseObject
+    field :id, ID, null: false
+    field :name, String
+
+    field :posts, [ Types::PostType ], null: false do
+      argument :use_cache, Boolean, required: true
+    end
+    def posts(use_cache:)
+      if use_cache
+        cache_fragment(expires_in: 1.minute) do
+          dataloader.with(Sources::PostsByUser).load(object.id)
+        end
+      else
+        dataloader.with(Sources::PostsByUser).load(object.id)
+      end
+    end
+  end
+end