Extend serializer lookup to the parent serializer.

lib/active_model/serializer.rb

@@ -108,10 +108,25 @@ module ActiveModel
       Digest::MD5.hexdigest(serializer_file_contents)
     end
 
+    # @api private
+    def self.serializer_lookup_chain_for(klass)
+      chain = []
+
+      resource_class_name = klass.name.demodulize
+      resource_namespace = klass.name.deconstantize
+      serializer_class_name = "#{resource_class_name}Serializer"
+
+      chain.push("#{name}::#{serializer_class_name}") if self != ActiveModel::Serializer
+      chain.push("#{resource_namespace}::#{serializer_class_name}")
+
+      chain
+    end
+
+    # @api private
     def self.get_serializer_for(klass)
       serializers_cache.fetch_or_store(klass) do
-        serializer_class_name = "#{klass.name}Serializer"
-        serializer_class = serializer_class_name.safe_constantize
+        # NOTE(beauby): When we drop 1.9.3 support we can lazify the map for perfs.
+        serializer_class = serializer_lookup_chain_for(klass).map(&:safe_constantize).find { |x| x }
 
         if serializer_class
           serializer_class

lib/active_model/serializer/array_serializer.rb

@@ -11,9 +11,8 @@ module ActiveModel
         @root = options[:root]
         @object = resources
         @serializers = resources.map do |resource|
-          serializer_class = options.fetch(:serializer) do
-            ActiveModel::Serializer.serializer_for(resource)
-          end
+          serializer_context_class = options.fetch(:serializer_context_class, ActiveModel::Serializer)
+          serializer_class = options.fetch(:serializer) { serializer_context_class.serializer_for(resource) }
 
           if serializer_class.nil?
             fail NoSerializerError, "No serializer found for resource: #{resource.inspect}"

lib/active_model/serializer/reflection.rb

@@ -42,13 +42,13 @@ module ActiveModel
       def build_association(subject, parent_serializer_options)
         association_value = subject.send(name)
         reflection_options = options.dup
-        serializer_class = ActiveModel::Serializer.serializer_for(association_value, reflection_options)
+        serializer_class = subject.class.serializer_for(association_value, reflection_options)
 
         if serializer_class
           begin
             serializer = serializer_class.new(
               association_value,
-              serializer_options(parent_serializer_options, reflection_options)
+              serializer_options(subject, parent_serializer_options, reflection_options)
             )
           rescue ActiveModel::Serializer::ArraySerializer::NoSerializerError
             reflection_options[:virtual_value] = association_value.try(:as_json) || association_value
@@ -62,11 +62,12 @@ module ActiveModel
 
       private
 
-      def serializer_options(parent_serializer_options, reflection_options)
+      def serializer_options(subject, parent_serializer_options, reflection_options)
         serializer = reflection_options.fetch(:serializer, nil)
 
         serializer_options = parent_serializer_options.except(:serializer)
         serializer_options[:serializer] = serializer if serializer
+        serializer_options[:serializer_context_class] = subject.class
         serializer_options
       end
     end