Add DSL for assocations

lib/active_model/serializer.rb

@@ -2,16 +2,18 @@ module ActiveModel
   class Serializer
     class << self
       attr_accessor :_attributes
+      attr_accessor :_associations
     end
 
     def self.inherited(base)
       base._attributes = []
+      base._associations = {}
     end
 
     def self.attributes(*attrs)
       @_attributes.concat attrs
 
-      
+
       attrs.each do |attr|
         define_method attr do
           object.read_attribute_for_serialization(attr)
@@ -19,6 +21,41 @@ module ActiveModel
       end
     end
 
+    # Defines an association in the object should be rendered.
+    #
+    # The serializer object should implement the association name
+    # as a method which should return an array when invoked. If a method
+    # with the association name does not exist, the association name is
+    # dispatched to the serialized object.
+    def self.has_many(*attrs)
+      associate(:has_many, attrs)
+    end
+
+    # Defines an association in the object should be rendered.
+    #
+    # The serializer object should implement the association name
+    # as a method which should return an object when invoked. If a method
+    # with the association name does not exist, the association name is
+    # dispatched to the serialized object.
+    def self.belongs_to(*attrs)
+      associate(:belongs_to, attrs)
+    end
+
+    def self.associate(type, attrs) #:nodoc:
+      options = attrs.extract_options!
+      self._associations = _associations.dup
+
+      attrs.each do |attr|
+        unless method_defined?(attr)
+          define_method attr do
+            object.send attr
+          end
+        end
+
+        self._associations[attr] = {type: type, options: options}
+      end
+    end
+
     if RUBY_VERSION >= '2.0'
       def self.serializer_for(resource)
         if resource.respond_to?(:to_ary)

test/serializers/associations_test.rb

@@ -0,0 +1,65 @@
+require 'test_helper'
+
+module ActiveModel
+  class Serializer
+    class AssocationsTest < Minitest::Test
+      def def_serializer(&block)
+        Class.new(ActiveModel::Serializer, &block)
+      end
+
+      class Model
+        def initialize(hash={})
+          @attributes = hash
+        end
+
+        def read_attribute_for_serialization(name)
+          @attributes[name]
+        end
+
+        def method_missing(meth, *args)
+          if meth.to_s =~ /^(.*)=$/
+            @attributes[$1.to_sym] = args[0]
+          elsif @attributes.key?(meth)
+            @attributes[meth]
+          else
+            super
+          end
+        end
+      end
+
+      def setup
+        @post = Model.new({ title: 'New Post', body: 'Body' })
+        @comment = Model.new({ id: 1, body: 'ZOMG A COMMENT' })
+        @post.comments = [@comment]
+        @comment.post = @post
+
+        @post_serializer_class = def_serializer do
+          attributes :title, :body
+        end
+
+        @comment_serializer_class = def_serializer do
+          attributes :id, :body
+        end
+
+        @post_serializer = @post_serializer_class.new(@post)
+        @comment_serializer = @comment_serializer_class.new(@comment)
+      end
+
+      def test_has_many
+        @post_serializer_class.class_eval do
+          has_many :comments
+        end
+
+        assert_equal({comments: {type: :has_many, options: {}}}, @post_serializer.class._associations)
+      end
+
+      def test_has_one
+        @comment_serializer_class.class_eval do
+          belongs_to :post
+        end
+
+        assert_equal({post: {type: :belongs_to, options: {}}}, @comment_serializer.class._associations)
+      end
+    end
+  end
+end