Adding Fragment Cache to AMS

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

Author: joaomdmoura

CHANGELOG.md

@@ -4,3 +4,5 @@
   * adds method to override association [adcb99e, @kurko]
   * adds `has_one` attribute for backwards compatibility [@ggordon]
   * updates JSON API support to RC3 [@mateomurphy]
+  * adds fragment cache support [@joaomdmoura]
+  * adds cache support to attributes and associations [@joaomdmoura]

README.md

@@ -271,7 +271,10 @@ The options are the same options of ```ActiveSupport::Cache::Store```, plus
 a ```key``` option that will be the prefix of the object cache
 on a pattern ```"#{key}/#{object.id}-#{object.updated_at}"```.
 
+The cache support is optimized to use the cached object in multiple request. An object cached on an ```show``` request will be reused at the ```index```. If there is a relationship with another cached serializer it will also be created and reused automatically.
+
 **[NOTE] Every object is individually cached.**
+
 **[NOTE] The cache is automatically expired after update an object but it's not deleted.**
 
 ```ruby
@@ -295,6 +298,27 @@ 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 by using ```only``` or ```except``` option on cache method.
+
+**[NOTE] Cache serializers will be used at their relationships**
+
+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

@@ -10,41 +10,54 @@ class Serializer
 
     class << self
       attr_accessor :_attributes
+      attr_accessor :_attributes_keys
       attr_accessor :_associations
       attr_accessor :_urls
       attr_accessor :_cache
+      attr_accessor :_fragmented
       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|
         define_method attr do
           object && object.read_attribute_for_serialization(attr)
-        end unless method_defined?(attr)
+        end unless method_defined?(attr) || _fragmented.respond_to?(attr)
       end
     end
 
     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)
-      end unless method_defined?(key)
+      end unless method_defined?(key) || _fragmented.respond_to?(attr)
+    end
+
+    def self.fragmented(serializer)
+      @_fragmented = serializer
     end
 
     # Enables a serializer to be automatically cached
     def self.cache(options = {})
-      @_cache = ActionController::Base.cache_store if Rails.configuration.action_controller.perform_caching
-      @_cache_key = options.delete(:key)
+      @_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
 
@@ -141,12 +154,12 @@ def self.root_name
     attr_accessor :object, :root, :meta, :meta_key, :scope
 
     def initialize(object, options = {})
-      @object   = object
-      @options  = options
-      @root     = options[:root] || (self.class._root ? self.class.root_name : false)
-      @meta     = options[:meta]
-      @meta_key = options[:meta_key]
-      @scope    = options[:scope]
+      @object     = object
+      @options    = options
+      @root       = options[:root] || (self.class._root ? self.class.root_name : false)
+      @meta       = options[:meta]
+      @meta_key   = options[:meta_key]
+      @scope      = options[:scope]
 
       scope_name = options[:scope_name]
       if scope_name && !respond_to?(scope_name)
@@ -183,22 +196,29 @@ def attributes(options = {})
       attributes += options[:required_fields] if options[:required_fields]
 
       attributes.each_with_object({}) do |name, hash|
-        hash[name] = send(name)
+        unless self.class._fragmented
+          hash[name] = send(name)
+        else
+          hash[name] = self.class._fragmented.public_send(name)
+        end
       end
     end
 
     def each_association(&block)
       self.class._associations.dup.each do |name, association_options|
         next unless object
-
         association_value = send(name)
 
         serializer_class = ActiveModel::Serializer.serializer_for(association_value, association_options)
 
-        serializer = serializer_class.new(
-          association_value,
-          options.merge(serializer_from_options(association_options))
-        ) if serializer_class
+        if serializer_class
+          serializer = serializer_class.new(
+            association_value,
+            options.merge(serializer_from_options(association_options))
+          )
+        elsif !association_value.nil? && !association_value.instance_of?(Object)
+          association_options[:association_options][:virtual_value] = association_value
+        end
 
         if block_given?
           block.call(name, serializer, association_options[:association_options])

lib/active_model/serializer/adapter.rb

@@ -1,3 +1,5 @@
+require 'active_model/serializer/adapter/fragment_cache'
+
 module ActiveModel
   class Serializer
     class Adapter
@@ -32,8 +34,38 @@ def self.adapter_class(adapter)
         "ActiveModel::Serializer::Adapter::#{adapter.to_s.classify}".safe_constantize
       end
 
+      def fragment_cache(*args)
+        raise NotImplementedError, 'This is an abstract method. Should be implemented at the concrete adapter.'
+      end
+
       private
 
+      def cache_check(serializer)
+        @serializer = serializer
+        @klass      = serializer.class
+        if is_cached?
+          @klass._cache.fetch(cache_key, @klass._cache_options) do
+            yield
+          end
+        elsif is_fragment_cached?
+          FragmentCache.new(self, @serializer, @options, @root).fetch
+        else
+          yield
+        end
+      end
+
+      def is_cached?
+        @klass._cache && !@klass._cache_only && !@klass._cache_except
+      end
+
+      def is_fragment_cached?
+        @klass._cache_only && !@klass._cache_except || !@klass._cache_only && @klass._cache_except
+      end
+
+      def cache_key
+        (@klass._cache_key) ? "#{@klass._cache_key}/#{@serializer.object.id}-#{@serializer.object.updated_at}" : @serializer.object.cache_key
+      end
+
       def meta
         serializer.meta if serializer.respond_to?(:meta)
       end
@@ -50,20 +82,6 @@ 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/fragment_cache.rb

@@ -0,0 +1,78 @@
+module ActiveModel
+  class Serializer
+    class Adapter
+      class FragmentCache
+
+        attr_reader :serializer
+
+        def initialize(adapter, serializer, options, root)
+          @root       = root
+          @options    = options
+          @adapter    = adapter
+          @serializer = serializer
+        end
+
+        def fetch
+          klass = serializer.class
+          # It will split the serializer into two, one that will be cached and other wont
+          serializers = fragment_serializer(serializer.object.class.name, klass)
+
+          # Instanciate both serializers
+          cached_serializer     = serializers[:cached].constantize.new(serializer.object)
+          non_cached_serializer = serializers[:non_cached].constantize.new(serializer.object)
+
+          cached_adapter     = @adapter.class.new(cached_serializer, @options)
+          non_cached_adapter = @adapter.class.new(non_cached_serializer, @options)
+
+          # Get serializable hash from both
+          cached_hash     = cached_adapter.serializable_hash
+          non_cached_hash = non_cached_adapter.serializable_hash
+
+          # Merge both results
+          @adapter.fragment_cache(cached_hash, non_cached_hash)
+        end
+
+        private
+
+        def cached_attributes(klass, serializers)
+          cached_attributes     = (klass._cache_only) ? klass._cache_only : serializer.attributes.keys.delete_if {|attr| klass._cache_except.include?(attr) }
+          non_cached_attributes = serializer.attributes.keys.delete_if {|attr| cached_attributes.include?(attr) }
+
+          cached_attributes.each do |attribute|
+            options = serializer.class._attributes_keys[attribute]
+            options ||= {}
+            # Add cached attributes to cached Serializer
+            serializers[:cached].constantize.attribute(attribute, options)
+          end
+
+          non_cached_attributes.each do |attribute|
+            options = serializer.class._attributes_keys[attribute]
+            options ||= {}
+            # Add non-cached attributes to non-cached Serializer
+            serializers[:non_cached].constantize.attribute(attribute, options)
+          end
+        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)
+
+          cached.constantize.fragmented(serializer)
+          non_cached.constantize.fragmented(serializer)
+
+          serializers = {cached: cached, non_cached: non_cached}
+          cached_attributes(klass, serializers)
+          serializers
+        end
+      end
+    end
+  end
+end

lib/active_model/serializer/adapter/json.rb

@@ -1,3 +1,5 @@
+require 'active_model/serializer/adapter/json/fragment_cache'
+
 module ActiveModel
   class Serializer
     class Adapter
@@ -6,31 +8,45 @@ def serializable_hash(options = {})
           if serializer.respond_to?(:each)
             @result = serializer.map{|s| self.class.new(s).serializable_hash }
           else
-            @result = cached_object do
-              @hash = serializer.attributes(options)
-              serializer.each_association do |name, association, opts|
-                if association.respond_to?(:each)
-                  array_serializer = association
-                  @hash[name] = array_serializer.map { |item| item.attributes(opts) }
-                else
-                  if association
-                    @hash[name] = association.attributes(options)
-                  else
-                    @hash[name] = nil
+            @hash = {}
+
+            @core = cache_check(serializer) do
+              serializer.attributes(options)
+            end
+
+            serializer.each_association do |name, association, opts|
+              if association.respond_to?(:each)
+                array_serializer = association
+                @hash[name] = array_serializer.map do |item|
+                  cache_check(item) do
+                    item.attributes(opts)
                   end
                 end
+              else
+                if association
+                  @hash[name] = cache_check(association) do
+                    association.attributes(options)
+                  end
+                elsif opts[:virtual_value]
+                  @hash[name] = opts[:virtual_value]
+                else
+                  @hash[name] = nil
+                end
               end
-              @hash
             end
+            @result = @core.merge @hash
           end
 
           if root = options.fetch(:root, serializer.json_key)
             @result = { root => @result }
           end
-
           @result
         end
       end
+
+      def fragment_cache(cached_hash, non_cached_hash)
+        Json::FragmentCache.new().fragment_cache(cached_hash, non_cached_hash)
+      end
     end
   end
-end
+end

lib/active_model/serializer/adapter/json/fragment_cache.rb

@@ -0,0 +1,15 @@
+module ActiveModel
+  class Serializer
+    class Adapter
+      class Json < Adapter
+        class FragmentCache
+
+          def fragment_cache(cached_hash, non_cached_hash)
+            non_cached_hash.merge cached_hash
+          end
+
+        end
+      end
+    end
+  end
+end