Default the generated cache key to use custom #strftime instead of raw #to_s to achieve more accurate precision

lib/active_model/serializer/adapter.rb

@@ -72,7 +72,9 @@ module ActiveModel
       end
 
       def object_cache_key
-        (@klass._cache_key) ? "#{@klass._cache_key}/#{@cached_serializer.object.id}-#{@cached_serializer.object.updated_at}" : @cached_serializer.object.cache_key
+        object_time_safe = @cached_serializer.object.updated_at
+        object_time_safe = object_time_safe.strftime("%Y%m%d%H%M%S%9N") if object_time_safe.respond_to?(:strftime)
+        (@klass._cache_key) ? "#{@klass._cache_key}/#{@cached_serializer.object.id}-#{object_time_safe}" : @cached_serializer.object.cache_key
       end
 
       def meta

test/action_controller/serialization_test.rb

@@ -98,13 +98,12 @@ module ActionController
 
         def render_fragment_changed_object_with_relationship
           comment = Comment.new({ id: 1, body: 'ZOMG A COMMENT' })
+          comment2 = Comment.new({ id: 1, body: 'ZOMG AN UPDATED-BUT-NOT-CACHE-EXPIRED COMMENT' })
           author = Author.new(id: 1, name: 'Joao Moura.')
-          post = Post.new({ id: 1, title: 'New Post', body: 'Body', comments: [comment], author: author })
+          like = Like.new({ id: 1, likeable: comment, time: 3.days.ago })
-          post2 = Post.new({ id: 1, title: 'New Post2', body: 'Body2', comments: [comment], author: author })
-          like = Like.new({ id: 1, post: post, time: 3.days.ago })
 
           generate_cached_serializer(like)
-          like.post = post2
+          like.likable = comment2
           like.time = DateTime.now.to_s
 
           render json: like
@@ -229,7 +228,7 @@ module ActionController
         assert_equal expected.to_json, @response.body
 
         get :render_changed_object_with_cache_enabled
-        assert_equal expected.to_json, @response.body
+        assert_not_equal expected.to_json, @response.body
 
         ActionController::Base.cache_store.clear
         get :render_changed_object_with_cache_enabled
@@ -291,10 +290,9 @@ module ActionController
         expected_return = {
           "id"=>1,
           "time"=>DateTime.now.to_s,
-          "post" => {
+          "likeable" => {
             "id"=>1,
-            "title"=>"New Post",
+            "body"=>"ZOMG A COMMENT"
-            "body"=>"Body"
           }
         }
 

test/fixtures/poro.rb

@@ -10,7 +10,7 @@ class Model
   end
 
   def cache_key
-    "#{self.class.name.downcase}/#{self.id}-#{self.updated_at}"
+    "#{self.class.name.downcase}/#{self.id}-#{self.updated_at.strftime("%Y%m%d%H%M%S%9N")}"
   end
 
   def cache_key_with_digest
@@ -18,7 +18,7 @@ class Model
   end
 
   def updated_at
-    @attributes[:updated_at] ||= DateTime.now.to_time.to_i
+    @attributes[:updated_at] ||= DateTime.now.to_time
   end
 
   def read_attribute_for_serialization(name)
@@ -69,7 +69,6 @@ end
 
 Post     = Class.new(Model)
 Like     = Class.new(Model)
-Comment  = Class.new(Model)
 Author   = Class.new(Model)
 Bio      = Class.new(Model)
 Blog     = Class.new(Model)
@@ -77,6 +76,12 @@ Role     = Class.new(Model)
 User     = Class.new(Model)
 Location = Class.new(Model)
 Place    = Class.new(Model)
+Comment  = Class.new(Model) do
+  # Uses a custom non-time-based cache key
+  def cache_key
+    "#{self.class.name.downcase}/#{self.id}"
+  end
+end
 
 module Spam; end
 Spam::UnrelatedLink = Class.new(Model)
@@ -143,7 +148,7 @@ end
 LikeSerializer = Class.new(ActiveModel::Serializer) do
   attributes :id, :time
 
-  belongs_to :post
+  belongs_to :likeable
 end
 
 LocationSerializer = Class.new(ActiveModel::Serializer) do

test/serializers/cache_test.rb

@@ -48,7 +48,7 @@ module ActiveModel
       def test_cache_key_interpolation_with_updated_at
         author = render_object_with_cache(@author)
         assert_equal(nil, ActionController::Base.cache_store.fetch(@author.cache_key))
-        assert_equal(@author_serializer.attributes.to_json, ActionController::Base.cache_store.fetch("#{@author_serializer.class._cache_key}/#{@author_serializer.object.id}-#{@author_serializer.object.updated_at}").to_json)
+        assert_equal(@author_serializer.attributes.to_json, ActionController::Base.cache_store.fetch("#{@author_serializer.class._cache_key}/#{@author_serializer.object.id}-#{@author_serializer.object.updated_at.strftime("%Y%m%d%H%M%S%9N")}").to_json)
       end
 
       def test_default_cache_key_fallback
@@ -85,7 +85,7 @@ module ActiveModel
         # Generate a new Cache of Post object and each objects related to it.
         render_object_with_cache(@post)
 
-        # Check if if cache the objects separately
+        # Check if it cached the objects separately
         assert_equal(@post_serializer.attributes, ActionController::Base.cache_store.fetch(@post.cache_key))
         assert_equal(@comment_serializer.attributes, ActionController::Base.cache_store.fetch(@comment.cache_key))