fix for serializers never including associations on cache hits

lib/active_model/serializer.rb

@@ -353,13 +353,16 @@ def as_json(options={})
     # Returns a hash representation of the serializable
     # object without the root.
     def serializable_hash
-      if perform_caching?
+      @node = if perform_caching?
         cache.fetch expand_cache_key([self.class.to_s.underscore, cache_key, 'serializable-hash']) do
           _serializable_hash
         end
       else
         _serializable_hash
       end
+
+      include_associations! if @object.present? && _embed
+      @node
     end
 
     def include_associations!
@@ -476,9 +479,7 @@ def scope
 
     def _serializable_hash
       return nil if @object.nil?
-      @node = attributes
-      include_associations! if _embed
-      @node
+      attributes
     end
 
     def perform_caching?

test/caching_test.rb

@@ -35,6 +35,42 @@ def read_attribute_for_serialization(name)
     end
   end
 
+  class Parent
+    def id
+      'parent1'
+    end
+
+    def name
+      'Kieran'
+    end
+
+    def children
+      [ Child.new ]
+    end
+
+    def read_attribute_for_serialization(name)
+      send name
+    end
+  end
+
+  class Child
+    def id
+      'child1'
+    end
+
+    def name
+      'Joshua'
+    end
+
+    def parent
+      Parent.new
+    end
+
+    def read_attribute_for_serialization(name)
+      send name
+    end
+  end
+
   def test_serializers_have_a_cache_store
     ActiveModel::Serializer.cache = NullStore.new
 
@@ -93,4 +129,49 @@ def cache_key
     assert_equal instance.serializable_array, serializer.cache.read('array_serializer/cache-key/serializable-array')
     assert_equal instance.to_json, serializer.cache.read('array_serializer/cache-key/to-json')
   end
+
+  def test_cached_serializers_return_associations
+
+    child_serializer = Class.new(ActiveModel::Serializer) do
+      cached true
+      attributes :name
+
+      def self.to_s
+        'child_serializer'
+      end
+
+      def cache_key
+        object.name
+      end
+    end
+
+    parent_serializer = Class.new(ActiveModel::Serializer) do
+      cached true
+      attributes :name
+
+      has_many :children, serializer: child_serializer, embed: :ids, include: true
+
+      def self.to_s
+        'parent_serializer'
+      end
+
+      def cache_key
+        object.name
+      end
+    end
+
+
+    parent_serializer.cache = NullStore.new
+    child_serializer.cache = NullStore.new
+
+    instance = parent_serializer.new Parent.new, root: :parent
+
+    initial_keys = instance.as_json.keys
+
+    assert_equal(initial_keys, [:children, :parent])
+
+    cached_keys = instance.as_json.keys
+
+    assert_equal(cached_keys, [:children, :parent])
+  end
 end