Associations refactoring

* Move all associations related code from Serializer class to Associations module
* Introduce Reflection class hierarchy
* Introduce Association class
* Rid off Serializer#each_association
* Introduce Serializer#associations enumerator

lib/active_model/serializer/adapter/json.rb

@@ -7,7 +7,7 @@ module ActiveModel
         def serializable_hash(options = nil)
           options ||= {}
           if serializer.respond_to?(:each)
-            @result = serializer.map{|s| FlattenJson.new(s).serializable_hash(options) }
+            @result = serializer.map { |s| FlattenJson.new(s).serializable_hash(options) }
           else
             @hash = {}
 
@@ -15,24 +15,26 @@ module ActiveModel
               serializer.attributes(options)
             end
 
-            serializer.each_association do |key, association, opts|
-              if association.respond_to?(:each)
-                array_serializer = association
-                @hash[key] = array_serializer.map do |item|
+            serializer.associations.each do |association|
+              serializer = association.serializer
+              opts = association.options
+
+              if serializer.respond_to?(:each)
+                array_serializer = serializer
+                @hash[association.key] = array_serializer.map do |item|
                   cache_check(item) do
                     item.attributes(opts)
                   end
                 end
               else
-                if association && association.object
-                  @hash[key] = cache_check(association) do
-                    association.attributes(options)
+                @hash[association.key] =
+                  if serializer && serializer.object
+                    cache_check(serializer) do
+                      serializer.attributes(options)
+                    end
+                  elsif opts[:virtual_value]
+                    opts[:virtual_value]
                   end
-                elsif opts[:virtual_value]
-                  @hash[key] = opts[:virtual_value]
-                else
-                  @hash[key] = nil
-                end
               end
             end
             @result = @core.merge @hash

lib/active_model/serializer/adapter/json_api.rb

@@ -75,8 +75,10 @@ module ActiveModel
           end
 
           serializers.each do |serializer|
-            serializer.each_association do |key, association, opts|
-              add_included(key, association, resource_path) if association
+            serializer.associations.each do |association|
+              serializer = association.serializer
+
+              add_included(association.key, serializer, resource_path) if serializer
             end if include_nested_assoc? resource_path
           end
         end
@@ -131,22 +133,26 @@ module ActiveModel
         def add_resource_relationships(attrs, serializer, options = {})
           options[:add_included] = options.fetch(:add_included, true)
 
-          serializer.each_association do |key, association, opts|
+          serializer.associations.each do |association|
+            key = association.key
+            serializer = association.serializer
+            opts = association.options
+
             attrs[:relationships] ||= {}
 
-            if association.respond_to?(:each)
-              add_relationships(attrs, key, association)
+            if serializer.respond_to?(:each)
+              add_relationships(attrs, key, serializer)
             else
               if opts[:virtual_value]
                 add_relationship(attrs, key, nil, opts[:virtual_value])
               else
-                add_relationship(attrs, key, association)
+                add_relationship(attrs, key, serializer)
               end
             end
 
             if options[:add_included]
-              Array(association).each do |association|
-                add_included(key, association)
+              Array(serializer).each do |serializer|
+                add_included(key, serializer)
               end
             end
           end