Ensuring read_multi works with fragment cache.

CHANGELOG.md

@@ -7,6 +7,7 @@ Breaking changes:
 Features:
 
 Fixes:
+- [#1814] (https://github.com/rails-api/active_model_serializers/pull/1814) Ensuring read_multi works with fragment cache
 
 Misc:
 

lib/active_model/serializer/caching.rb

@@ -197,7 +197,7 @@ def object_cache_keys(collection_serializer, adapter_instance, include_directive
         def object_cache_key(serializer, adapter_instance)
           return unless serializer.present? && serializer.object.present?
 
-          serializer.class.cache_enabled? ? serializer.cache_key(adapter_instance) : nil
+          (serializer.class.cache_enabled? || serializer.class.fragment_cache_enabled?) ? serializer.cache_key(adapter_instance) : nil
         end
       end
 
@@ -211,7 +211,7 @@ def fetch_attributes(fields, cached_attributes, adapter_instance)
             end
           end
         elsif serializer_class.fragment_cache_enabled?
-          fetch_attributes_fragment(adapter_instance)
+          fetch_attributes_fragment(adapter_instance, cached_attributes)
         else
           attributes(fields, true)
         end
@@ -227,28 +227,34 @@ def fetch(adapter_instance, cache_options = serializer_class._cache_options)
         end
       end
 
+      def non_cached_attributes(adapter_instance, fields)
+        non_cached_fields = fields[:non_cached].dup
+        non_cached_hash = attributes(non_cached_fields, true)
+        include_directive = JSONAPI::IncludeDirective.new(non_cached_fields - non_cached_hash.keys)
+        non_cached_hash.merge! resource_relationships({}, { include_directive: include_directive }, adapter_instance)
+        non_cached_hash
+      end
+
       # 1. Determine cached fields from serializer class options
       # 2. Get non_cached_fields and fetch cache_fields
       # 3. Merge the two hashes using adapter_instance#fragment_cache
-      def fetch_attributes_fragment(adapter_instance)
+      def fetch_attributes_fragment(adapter_instance, cached_attributes = {})
         serializer_class._cache_options ||= {}
         serializer_class._cache_options[:key] = serializer_class._cache_key if serializer_class._cache_key
         fields = serializer_class.fragmented_attributes
 
-        non_cached_fields = fields[:non_cached].dup
-        non_cached_hash = attributes(non_cached_fields, true)
-        include_directive = JSONAPI::IncludeDirective.new(non_cached_fields - non_cached_hash.keys)
-        non_cached_hash.merge! resource_relationships({}, { include_directive: include_directive }, adapter_instance)
+        non_cached_hash = non_cached_attributes(adapter_instance, fields)
 
         cached_fields = fields[:cached].dup
         key = cache_key(adapter_instance)
         cached_hash =
-          serializer_class.cache_store.fetch(key, serializer_class._cache_options) do
-            hash = attributes(cached_fields, true)
-            include_directive = JSONAPI::IncludeDirective.new(cached_fields - hash.keys)
-            hash.merge! resource_relationships({}, { include_directive: include_directive }, adapter_instance)
+          cached_attributes.fetch(key) do
+            serializer_class.cache_store.fetch(key, serializer_class._cache_options) do
+              hash = attributes(cached_fields, true)
+              include_directive = JSONAPI::IncludeDirective.new(cached_fields - hash.keys)
+              hash.merge! resource_relationships({}, { include_directive: include_directive }, adapter_instance)
+            end
           end
-
         # Merge both results
         adapter_instance.fragment_cache(cached_hash, non_cached_hash)
       end

test/cache_test.rb

@@ -321,6 +321,36 @@ def test_fetch_attributes_from_cache
       end
     end
 
+    def test_cache_read_multi_with_fragment_cache_enabled
+      post_serializer = Class.new(ActiveModel::Serializer) do
+        cache except: [:body]
+      end
+
+      serializers = ActiveModel::Serializer::CollectionSerializer.new([@post, @post], serializer: post_serializer)
+
+      Timecop.freeze(Time.current) do
+        # Warming up.
+        options = {}
+        adapter_options = {}
+        adapter_instance = ActiveModelSerializers::Adapter::Attributes.new(serializers, adapter_options)
+        serializers.serializable_hash(adapter_options, options, adapter_instance)
+
+        # Should find something with read_multi now
+        options = {}
+        adapter_options = {}
+        adapter_instance = ActiveModelSerializers::Adapter::Attributes.new(serializers, adapter_options)
+        serializers.serializable_hash(adapter_options, options, adapter_instance)
+        cached_attributes = adapter_options.fetch(:cached_attributes)
+
+        include_directive = ActiveModelSerializers.default_include_directive
+        manual_cached_attributes = ActiveModel::Serializer.cache_read_multi(serializers, adapter_instance, include_directive)
+
+        refute_equal 0, cached_attributes.size
+        refute_equal 0, manual_cached_attributes.size
+        assert_equal manual_cached_attributes, cached_attributes
+      end
+    end
+
     def test_serializer_file_path_on_nix
       path = '/Users/git/emberjs/ember-crm-backend/app/serializers/lead_serializer.rb'
       caller_line = "#{path}:1:in `<top (required)>'"