Implement has_one's and serialize_ids

lib/active_model/serializer.rb

@@ -1,15 +1,18 @@
+require 'active_model/serializer/associations'
+
 module ActiveModel
   class Serializer
     class << self
       def inherited(base)
-        base._attributes = {}
+        base._attributes = []
+        base._associations = []
       end
 
       def serializer_for(resource)
         "#{resource.class.name}Serializer".safe_constantize
       end
 
-      attr_accessor :_root, :_attributes
+      attr_accessor :_root, :_attributes, :_associations
 
       def root(root)
         @_root = root
@@ -21,7 +24,7 @@ module ActiveModel
       end
 
       def attributes(*attrs)
-        @_attributes = attrs.map(&:to_s)
+        @_attributes.concat attrs.map(&:to_s)
 
         attrs.each do |attr|
           unless method_defined?(attr)
@@ -31,6 +34,22 @@ module ActiveModel
           end
         end
       end
+
+      def has_one(*attrs)
+        options = attrs.extract_options!
+
+        attrs.each do |attr|
+          attr = attr.to_s
+
+          unless method_defined?(attr)
+            define_method attr do
+              object.send attr
+            end
+          end
+
+          @_associations << Association::HasOne.new(attr, options)
+        end
+      end
     end
 
     def initialize(object, options={})
@@ -51,9 +70,30 @@ module ActiveModel
       end
     end
 
+    def associations
+      self.class._associations.each_with_object({}) do |association, hash|
+        if association.embed_ids?
+          hash[association.key] = serialize_ids association
+        elsif association.embed_objects?
+          # TODO
+          hash
+        end
+      end
+    end
+
+    def serialize_ids(association)
+      associated_data = send(association.name)
+      if associated_data.respond_to?(:to_ary)
+        associated_data.map { |elem| elem.send(association.embed_key) }
+      else
+        associated_data.send(association.embed_key)
+      end
+    end
+
     def serializable_hash(options={})
       return nil if object.nil?
-      attributes
+      hash = attributes
+      hash.merge! associations
     end
 
     def as_json(options={})