sparse fieldsets

lib/action_controller/serialization.rb

@@ -6,7 +6,7 @@ module Serialization
 
     include ActionController::Renderers
 
-    ADAPTER_OPTION_KEYS = [:include, :root]
+    ADAPTER_OPTION_KEYS = [:include, :fields, :root]
 
     [:_render_option_json, :_render_with_renderer_json].each do |renderer_method|
       define_method renderer_method do |resource, options|

lib/active_model/serializer.rb

@@ -124,7 +124,14 @@ def json_key
     end
 
     def attributes(options = {})
-      self.class._attributes.dup.each_with_object({}) do |name, hash|
+      attributes =
+        if options[:fields]
+          self.class._attributes & options[:fields]
+        else
+          self.class._attributes.dup
+        end
+
+      attributes.each_with_object({}) do |name, hash|
         hash[name] = send(name)
       end
     end

lib/active_model/serializer/adapter/json_api.rb

@@ -7,14 +7,20 @@ def initialize(serializer, options = {})
           serializer.root = true
           @hash = {}
           @top = @options.fetch(:top) { @hash }
+
+          if fields = options.delete(:fields)
+            @fieldset = ActiveModel::Serializer::Fieldset.new(fields, serializer.json_key)
+          else
+            @fieldset = options[:fieldset]
+          end
         end
 
         def serializable_hash(options = {})
           @root = (@options[:root] || serializer.json_key.to_s.pluralize).to_sym
 
           if serializer.respond_to?(:each)
             @hash[@root] = serializer.map do |s|
-              self.class.new(s, @options.merge(top: @top)).serializable_hash[@root]
+              self.class.new(s, @options.merge(top: @top, fieldset: @fieldset)).serializable_hash[@root]
             end
           else
             @hash[@root] = attributes_for_serializer(serializer, @options)
@@ -93,6 +99,10 @@ def add_linked(resource, serializer, parent = nil)
         private
 
         def attributes_for_serializer(serializer, options)
+          if fields = @fieldset && @fieldset.fields_for(serializer)
+            options[:fields] = fields
+          end
+
           attributes = serializer.attributes(options)
           attributes[:id] = attributes[:id].to_s if attributes[:id]
           attributes

lib/active_model/serializer/fieldset.rb

@@ -0,0 +1,36 @@
+module ActiveModel
+  class Serializer
+    class Fieldset
+
+      attr_reader :fields, :root
+
+      def initialize(fields, root = nil)
+        @root   = root
+        @fields = parse(fields)
+      end
+
+      def fields_for(serializer)
+        key = serializer.json_key || serializer.class.root_name
+        fields[key.to_sym]
+      end
+
+    private
+
+      def parse(fields)
+        if fields.is_a?(Hash)
+          fields.inject({}) { |h,(k,v)| h[k.to_sym] = v.map(&:to_sym); h}
+        elsif fields.is_a?(Array)
+          if root.nil?
+            raise ArgumentError, 'The root argument must be specified if the fileds argument is an array.'
+          end
+          hash = {}
+          hash[root.to_sym] = fields.map(&:to_sym)
+          hash
+        else
+          {}
+        end
+      end
+
+    end
+  end
+end

lib/active_model_serializers.rb

@@ -1,6 +1,7 @@
 require "active_model"
 require "active_model/serializer/version"
 require "active_model/serializer"
+require "active_model/serializer/fieldset"
 
 begin
   require 'action_controller'

test/adapter/json_api/belongs_to_test.rb

@@ -34,6 +34,11 @@ def test_includes_linked_post
             assert_equal([{id: "42", title: 'New Post', body: 'Body'}], @adapter.serializable_hash[:linked][:posts])
           end
 
+          def test_limiting_linked_post_fields
+            @adapter = ActiveModel::Serializer::Adapter::JsonApi.new(@serializer, include: 'post', fields: {post: [:title]})
+            assert_equal([{title: 'New Post'}], @adapter.serializable_hash[:linked][:posts])
+          end
+
           def test_include_nil_author
             serializer = PostSerializer.new(@anonymous_post)
             adapter = ActiveModel::Serializer::Adapter::JsonApi.new(serializer)

test/adapter/json_api/collection_test.rb

@@ -25,6 +25,15 @@ def test_include_multiple_posts
                            { title: "New Post", body: "Body", id: "2", links: { comments: [], author: "1" } }
                          ], @adapter.serializable_hash[:posts])
           end
+
+          def test_limiting_fields
+            @adapter = ActiveModel::Serializer::Adapter::JsonApi.new(@serializer, fields: ['title'])
+            assert_equal([
+              { title: "Hello!!", links: { comments: [], author: "1" } },
+              { title: "New Post", links: { comments: [], author: "1" } }
+            ], @adapter.serializable_hash[:posts])
+          end
+
         end
       end
     end

test/adapter/json_api/has_many_test.rb

@@ -40,6 +40,14 @@ def test_includes_linked_comments
                          ], @adapter.serializable_hash[:linked][:comments])
           end
 
+          def test_limit_fields_of_linked_comments
+            @adapter = ActiveModel::Serializer::Adapter::JsonApi.new(@serializer, include: 'comments', fields: {comment: [:body]})
+            assert_equal([
+                           {body: 'ZOMG A COMMENT'},
+                           {body: 'ZOMG ANOTHER COMMENT'}
+                         ], @adapter.serializable_hash[:linked][:comments])
+          end
+
           def test_no_include_linked_if_comments_is_empty
             serializer = PostSerializer.new(@post_without_comments)
             adapter = ActiveModel::Serializer::Adapter::JsonApi.new(serializer)

test/serializers/attributes_test.rb

@@ -12,7 +12,11 @@ def test_attributes_definition
         assert_equal([:name, :description],
                      @profile_serializer.class._attributes)
       end
+
+      def test_attributes_with_fields_option
+        assert_equal({name: 'Name 1'},
+                     @profile_serializer.attributes( { fields: [:name] } ) )
+      end
     end
   end
 end
-

test/serializers/fieldset_test.rb

@@ -0,0 +1,26 @@
+require 'test_helper'
+
+module ActiveModel
+  class Serializer
+    class FieldsetTest < Minitest::Test
+
+      def test_fieldset_with_hash
+        fieldset = ActiveModel::Serializer::Fieldset.new({'post' => ['id', 'title'], 'coment' => ['body']})
+
+        assert_equal(
+          {:post=>[:id, :title], :coment=>[:body]}, 
+          fieldset.fields
+        )
+      end
+
+      def test_fieldset_with_array_of_fields_and_root_name
+        fieldset = ActiveModel::Serializer::Fieldset.new(['title'], 'post')
+
+        assert_equal(
+          {:post => [:title]}, 
+          fieldset.fields
+        )
+      end
+    end
+  end
+end