Fix CachingPostSerializer defining associations twice; add FragmentCaching benchmaking

test/benchmark/bm_caching.rb

@@ -31,6 +31,10 @@ def get_caching(on_off = 'on'.freeze)
     get("/caching/#{on_off}")
   end
 
+  def get_fragment_caching(on_off = 'on'.freeze)
+    get("/fragment_caching/#{on_off}")
+  end
+
   def get_non_caching(on_off = 'on'.freeze)
     get("/non_caching/#{on_off}")
   end
@@ -101,8 +105,10 @@ def assert_equal(expected, actual, message)
 time = 10
 {
   'caching on: caching serializers: gc off' => { disable_gc: true, send: [:get_caching, 'on'] },
+  'caching on: fragment caching serializers: gc off' => { disable_gc: true, send: [:get_fragment_caching, 'on'] },
   'caching on: non-caching serializers: gc off' => { disable_gc: true, send: [:get_non_caching, 'on'] },
   'caching off: caching serializers: gc off' => { disable_gc: true, send: [:get_caching, 'off'] },
+  'caching off: fragment caching serializers: gc off' => { disable_gc: true, send: [:get_fragment_caching, 'off'] },
   'caching off: non-caching serializers: gc off' => { disable_gc: true, send: [:get_non_caching, 'off'] }
 }.each do |label, options|
   assertion.clear

test/benchmark/controllers.rb

@@ -1,12 +1,13 @@
 class PostController < ActionController::Base
   POST =
     begin
+      updated_at = Time.current
       if ENV['BENCH_STRESS']
         comments = (0..50).map do |i|
-          Comment.new(id: i, body: 'ZOMG A COMMENT')
+          Comment.new(id: i, body: 'ZOMG A COMMENT', updated_at: updated_at + i)
         end
       else
-        comments = [Comment.new(id: 1, body: 'ZOMG A COMMENT')]
+        comments = [Comment.new(id: 1, body: 'ZOMG A COMMENT', updated_at: updated_at)]
       end
       author = Author.new(id: 42, first_name: 'Joao', last_name: 'Moura')
       Post.new(id: 1337, title: 'New Post', blog: nil, body: 'Body', comments: comments, author: author)
@@ -17,6 +18,11 @@ def render_with_caching_serializer
     render json: POST, serializer: CachingPostSerializer, adapter: :json, meta: { caching: perform_caching }
   end
 
+  def render_with_fragment_caching_serializer
+    toggle_cache_status
+    render json: POST, serializer: FragmentCachingPostSerializer, adapter: :json, meta: { caching: perform_caching }
+  end
+
   def render_with_non_caching_serializer
     toggle_cache_status
     render json: POST, adapter: :json, meta: { caching: perform_caching }
@@ -73,5 +79,6 @@ def toggle_cache_status
   get '/status(/:on)' => 'post#render_cache_status'
   get '/clear' => 'post#clear'
   get '/caching(/:on)' => 'post#render_with_caching_serializer'
+  get '/fragment_caching(/:on)' => 'post#render_with_fragment_caching_serializer'
   get '/non_caching(/:on)' => 'post#render_with_non_caching_serializer'
 end

test/benchmark/fixtures.rb

@@ -13,7 +13,7 @@ class BlogSerializer < ActiveModel::Serializer
 Rails.configuration.serializers << BlogSerializer
 
 class CommentSerializer < ActiveModel::Serializer
-  attributes :id, :body
+  attributes :id, :body, :updated_at
 
   belongs_to :post
   belongs_to :author
@@ -43,7 +43,7 @@ def blog
 Rails.configuration.serializers << PostSerializer
 
 class CachingAuthorSerializer < AuthorSerializer
-  cache key: 'writer', only: [:first_name, :last_name], skip_digest: true
+  cache key: 'writer', skip_digest: true
 end
 Rails.configuration.serializers << CachingAuthorSerializer
 
@@ -52,14 +52,66 @@ class CachingCommentSerializer < CommentSerializer
 end
 Rails.configuration.serializers << CachingCommentSerializer
 
-class CachingPostSerializer < PostSerializer
+# see https://github.com/rails-api/active_model_serializers/pull/1690/commits/68715b8f99bc29677e8a47bb3f305f23c077024b#r60344532
+class CachingPostSerializer < ActiveModel::Serializer
   cache key: 'post', expires_in: 0.1, skip_digest: true
+
+  attributes :id, :title, :body
+
   belongs_to :blog, serializer: BlogSerializer
   belongs_to :author, serializer: CachingAuthorSerializer
   has_many :comments, serializer: CachingCommentSerializer
+
+  link(:post_authors) { 'https://example.com/post_authors' }
+
+  meta do
+    {
+      rating: 5,
+      favorite_count: 10
+    }
+  end
+
+  def blog
+    Blog.new(id: 999, name: 'Custom blog')
+  end
 end
 Rails.configuration.serializers << CachingPostSerializer
 
+class FragmentCachingAuthorSerializer < AuthorSerializer
+  cache key: 'writer', only: [:first_name, :last_name], skip_digest: true
+end
+Rails.configuration.serializers << FragmentCachingAuthorSerializer
+
+class FragmentCachingCommentSerializer < CommentSerializer
+  cache expires_in: 1.day, except: [:updated_at], skip_digest: true
+end
+Rails.configuration.serializers << CachingCommentSerializer
+
+# see https://github.com/rails-api/active_model_serializers/pull/1690/commits/68715b8f99bc29677e8a47bb3f305f23c077024b#r60344532
+class FragmentCachingPostSerializer < ActiveModel::Serializer
+  cache key: 'post', expires_in: 0.1, skip_digest: true
+
+  attributes :id, :title, :body
+
+  belongs_to :blog, serializer: BlogSerializer
+  belongs_to :author, serializer: FragmentCachingAuthorSerializer
+  has_many :comments, serializer: FragmentCachingCommentSerializer
+
+  link(:post_authors) { 'https://example.com/post_authors' }
+
+  meta do
+    {
+      rating: 5,
+      favorite_count: 10
+    }
+  end
+
+  def blog
+    Blog.new(id: 999, name: 'Custom blog')
+  end
+end
+Rails.configuration.serializers << FragmentCachingPostSerializer
+
 if ENV['ENABLE_ACTIVE_RECORD'] == 'true'
   require 'active_record'
 
@@ -150,7 +202,7 @@ def read_attribute_for_serialization(key)
   end
 
   class Comment < BenchmarkModel
-    attr_accessor :id, :body
+    attr_accessor :id, :body, :updated_at
   end
 
   class Author < BenchmarkModel