Merge pull request #700 from arenoir/sparse_fieldsets

sparse fieldsets

lib/active_model/serializer/adapter/json_api.rb

@@ -7,6 +7,12 @@ module ActiveModel
           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 = {})
@@ -14,7 +20,7 @@ module ActiveModel
 
           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)
@@ -84,15 +90,18 @@ module ActiveModel
           end
         end
 
+
         def attributes_for_serializer(serializer, options)
           if serializer.respond_to?(:each)
             result = []
             serializer.each do |object|
+              options[:fields] = @fieldset && @fieldset.fields_for(serializer)
               attributes = object.attributes(options)
               attributes[:id] = attributes[:id].to_s if attributes[:id]
               result << attributes
             end
           else
+            options[:fields] = @fieldset && @fieldset.fields_for(serializer)
             result = serializer.attributes(options)
             result[:id] = result[:id].to_s if result[:id]
           end

lib/active_model/serializer/fieldset.rb

@@ -0,0 +1,40 @@
+module ActiveModel
+  class Serializer
+    class Fieldset
+
+      def initialize(fields, root = nil)
+        @root       = root
+        @raw_fields = fields
+      end
+
+      def fields
+        @fields ||= parsed_fields
+      end
+
+      def fields_for(serializer)
+        key = serializer.json_key || serializer.class.root_name
+        fields[key.to_sym]
+      end
+
+    private
+
+      attr_reader :raw_fields, :root
+
+      def parsed_fields
+        if raw_fields.is_a?(Hash)
+          raw_fields.inject({}) { |h,(k,v)| h[k.to_sym] = v.map(&:to_sym); h}
+        elsif raw_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] = raw_fields.map(&:to_sym)
+          hash
+        else
+          {}
+        end
+      end
+
+    end
+  end
+end