Adding Fragment Cache to AMS

It's an upgrade based on the new Cache implementation #693.
It allows to use the Rails conventions to cache
specific attributes or associations.
It's based on the Cache Composition implementation.

Author: joaomdmoura

README.md

@@ -271,6 +271,7 @@ a ```key``` option that will be the prefix of the object cache
 on a pattern ```"#{key}/#{object.id}-#{object.updated_at}"```.
 
 **[NOTE] Every object is individually cached.**
+
 **[NOTE] The cache is automatically expired after update an object but it's not deleted.**
 
 ```ruby
@@ -294,6 +295,25 @@ On this example every ```Post``` object will be cached with
 the key ```"post/#{post.id}-#{post.updated_at}"```. You can use this key to expire it as you want,
 but in this case it will be automatically expired after 3 hours.
 
+### Fragmenting Caching
+
+If there is some API endpoint that shouldn't be fully cached, you can still optmise it, using Fragment Cache on the attributes and relationships that you want to cache.
+
+You can define the attribute or relationships by using ```only``` or ```except``` option on cache method.
+
+Example:
+
+```ruby
+class PostSerializer < ActiveModel::Serializer
+  cache key: 'post', expires_in: 3.hours, only: [:title]
+  attributes :title, :body
+
+  has_many :comments
+
+  url :post
+end
+```
+
 ## Getting Help
 
 If you find a bug, please report an [Issue](https://github.com/rails-api/active_model_serializers/issues/new).

lib/active_model/serializer.rb

@@ -8,20 +8,25 @@ class Serializer
 
     class << self
       attr_accessor :_attributes
+      attr_accessor :_attributes_keys
       attr_accessor :_associations
       attr_accessor :_urls
       attr_accessor :_cache
       attr_accessor :_cache_key
+      attr_accessor :_cache_only
+      attr_accessor :_cache_except
       attr_accessor :_cache_options
     end
 
     def self.inherited(base)
       base._attributes = []
+      base._attributes_keys = {}
       base._associations = {}
       base._urls = []
     end
 
     def self.attributes(*attrs)
+      attrs = attrs.first if attrs.first.class == Array
       @_attributes.concat attrs
 
       attrs.each do |attr|
@@ -33,6 +38,7 @@ def self.attributes(*attrs)
 
     def self.attribute(attr, options = {})
       key = options.fetch(:key, attr)
+      @_attributes_keys[attr] = {key: key} if key != attr
       @_attributes.concat [key]
       define_method key do
         object.read_attribute_for_serialization(attr)
@@ -43,6 +49,8 @@ def self.attribute(attr, options = {})
     def self.cache(options = {})
       @_cache = ActionController::Base.cache_store if Rails.configuration.action_controller.perform_caching
       @_cache_key = options.delete(:key)
+      @_cache_only = options.delete(:only)
+      @_cache_except = options.delete(:except)
       @_cache_options = (options.empty?) ? nil : options
     end
 

lib/active_model/serializer/adapter.rb

@@ -1,7 +1,10 @@
+require 'active_model/serializer/cache'
+
 module ActiveModel
   class Serializer
     class Adapter
       extend ActiveSupport::Autoload
+      include ActiveModel::Serializer::Cache
       autoload :Json
       autoload :Null
       autoload :JsonApi
@@ -50,20 +53,6 @@ def include_meta(json)
         json[meta_key] = meta if meta && root
         json
       end
-
-      private
-
-      def cached_object
-        klass = serializer.class
-        if klass._cache
-          _cache_key = (klass._cache_key) ? "#{klass._cache_key}/#{serializer.object.id}-#{serializer.object.updated_at}" : serializer.object.cache_key
-          klass._cache.fetch(_cache_key, klass._cache_options) do
-            yield
-          end
-        else
-          yield
-        end
-      end
     end
   end
 end

lib/active_model/serializer/adapter/json_api.rb

@@ -91,7 +91,6 @@ def add_linked(resource_name, serializers, parent = nil)
           end
         end
 
-
         def attributes_for_serializer(serializer, options)
           if serializer.respond_to?(:each)
             result = []

lib/active_model/serializer/cache.rb

@@ -0,0 +1,100 @@
+module ActiveModel
+  class Serializer
+    module Cache
+      private
+      def cached_object
+        klass = serializer.class
+        if klass._cache && !klass._cache_only && !klass._cache_except
+          _cache_key = (klass._cache_key) ? "#{klass._cache_key}/#{serializer.object.id}-#{serializer.object.updated_at}" : serializer.object.cache_key
+          klass._cache.fetch(_cache_key, klass._cache_options) do
+            yield
+          end
+
+        elsif klass._cache_only && !klass._cache_except || !klass._cache_only && klass._cache_except
+          serializers = fragment_serializer(@serializer.object.class.name, klass)
+
+          cached_serializer = serializers[:cached].constantize.new(@serializer.object)
+          non_cached_serializer = serializers[:non_cached].constantize.new(@serializer.object)
+
+          cached_hash = self.class.new(cached_serializer, @options).serializable_hash
+          non_cached_hash = self.class.new(non_cached_serializer, @options).serializable_hash
+
+          if @serializer.root && self.class == ActiveModel::Serializer::Adapter::JsonApi
+            cached_hash_root(cached_hash, non_cached_hash)
+          else
+            non_cached_hash.merge cached_hash
+          end
+        else
+          yield
+        end
+      end
+
+      def cached_hash_root(cached_hash, non_cached_hash)
+        @root
+        hash = {}
+
+        core_cached = cached_hash.first
+        core_non_cached = non_cached_hash.first
+        no_root_cache = cached_hash.delete_if {|key, value| key == core_cached[0] }
+        no_root_non_cache = non_cached_hash.delete_if {|key, value| key == core_non_cached[0] }
+
+        if @root
+          hash[@root] = (core_cached[1]) ? core_cached[1].merge(core_non_cached[1]) : core_non_cached[1]
+        else
+          hash = (core_cached[1]) ? core_cached[1].merge(core_non_cached[1]) : core_non_cached[1]
+        end
+
+        hash.merge no_root_non_cache.merge no_root_cache
+      end
+
+      def fragment_associations(serializers, associations)
+        associations.each do |association|
+          options = ",#{association[1][:association_options]}" if association[1].include?(:association_options)
+          eval("#{serializers[:non_cached]}.#{association[1][:type].to_s}(:#{association[0]}#{options})")
+        end
+      end
+
+      def cached_attributes_and_association(klass, serializers)
+        cached_attr = (klass._cache_only) ? klass._cache_only : @serializer.attributes.keys.delete_if {|attr| klass._cache_except.include?(attr) }
+        non_cached_attr = @serializer.attributes.keys.delete_if {|attr| cached_attr.include?(attr) }
+        associations = @serializer.each_association
+
+        cached_attr.each do |attr|
+          if @serializer.each_association.keys.include?(attr)
+            associations.delete(attr)
+            serializers[:cached].constantize.send(@serializer.each_association[attr][:type], attr)
+          end
+        end
+
+        cached_attr.each do |attribute|
+          options = @serializer.class._attributes_keys[attribute]
+          options ||= {}
+          serializers[:cached].constantize.attribute(attribute, options)
+        end
+
+        non_cached_attr.each do |attribute|
+          options = @serializer.class._attributes_keys[attribute]
+          options ||= {}
+          serializers[:non_cached].constantize.attribute(attribute, options)
+        end
+        fragment_associations(serializers, associations)
+      end
+
+      def fragment_serializer(name, klass)
+        cached = "#{name.capitalize}CachedSerializer"
+        non_cached = "#{name.capitalize}NonCachedSerializer"
+
+        Object.const_set cached, Class.new(ActiveModel::Serializer) unless Object.const_defined?(cached)
+        Object.const_set non_cached, Class.new(ActiveModel::Serializer) unless Object.const_defined?(non_cached)
+
+        klass._cache_options ||= {}
+        klass._cache_options[:key] = klass._cache_key if klass._cache_key
+        cached.constantize.cache(klass._cache_options)
+
+        serializers = {cached: cached, non_cached: non_cached}
+        cached_attributes_and_association(klass, serializers)
+        return serializers
+      end
+    end
+  end
+end

test/action_controller/json_api_linked_test.rb

@@ -110,12 +110,14 @@ def test_render_resource_with_nested_has_many_include
           "roles"=>[{
             "id" => "1",
             "name" => "admin",
+            "description" => nil,
             "links" => {
               "author" => "1"
             }
           }, {
             "id" => "2",
             "name" => "colab",
+            "description" => nil,
             "links" => {
               "author" => "1"
             }

test/action_controller/serialization_test.rb

@@ -81,6 +81,42 @@ def render_changed_object_with_cache_enabled
           render json: post
         end
 
+        def render_fragment_changed_object_with_only_cache_enabled
+          author = Author.new(id: 1, name: 'Joao Moura.')
+          role = Role.new({ id: 42, name: 'ZOMG A ROLE', description: 'DESCRIPTION HERE', author: author })
+
+          generate_cached_serializer(role)
+          role.name = 'lol'
+          role.description = 'HUEHUEBRBR'
+
+          render json: role
+        end
+
+        def render_fragment_changed_object_with_except_cache_enabled
+          author = Author.new(id: 1, name: 'Joao Moura.')
+          bio = Bio.new({ id: 42, content: 'ZOMG A ROLE', rating: 5, author: author })
+
+          generate_cached_serializer(bio)
+          bio.content = 'lol'
+          bio.rating = 0
+
+          render json: bio
+        end
+
+        def render_fragment_changed_object_with_relationship
+          comment = Comment.new({ id: 1, body: 'ZOMG A COMMENT' })
+          author = Author.new(id: 1, name: 'Joao Moura.')
+          post = Post.new({ id: 1, title: 'New Post', blog:nil, body: 'Body', comments: [comment], author: author })
+          post2 = Post.new({ id: 1, title: 'New Post2', blog:nil, 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.time = DateTime.now.to_s
+
+          render json: like
+        end
+
         private
         def generate_cached_serializer(obj)
           serializer_class = ActiveModel::Serializer.serializer_for(obj)
@@ -200,6 +236,45 @@ def test_render_with_cache_enable_and_expired
         assert_equal 'application/json', @response.content_type
         assert_equal expected.to_json, @response.body
       end
+
+      def test_render_with_fragment_only_cache_enable
+        ActionController::Base.cache_store.clear
+        get :render_fragment_changed_object_with_only_cache_enabled
+        response = JSON.parse(@response.body)
+
+        assert_equal 'application/json', @response.content_type
+        assert_equal 'ZOMG A ROLE', response["name"]
+        assert_equal 'HUEHUEBRBR', response["description"]
+      end
+
+      def test_render_with_fragment_except_cache_enable
+        ActionController::Base.cache_store.clear
+        get :render_fragment_changed_object_with_except_cache_enabled
+        response = JSON.parse(@response.body)
+
+        assert_equal 'application/json', @response.content_type
+        assert_equal 5, response["rating"]
+        assert_equal 'lol', response["content"]
+      end
+
+      def test_render_fragment_changed_object_with_relationship
+        ActionController::Base.cache_store.clear
+        get :render_fragment_changed_object_with_relationship
+        response = JSON.parse(@response.body)
+
+        expected_return = {
+          "post" => {
+            "id"=>1,
+            "title"=>"New Post",
+            "body"=>"Body"
+          },
+          "id"=>1,
+          "time"=>DateTime.now.to_s
+        }
+
+        assert_equal 'application/json', @response.content_type
+        assert_equal expected_return, response
+      end
     end
   end
-end
+end