Mark cached value as persisted when is an instance of ActiveRecord::Base

lib/gitlab/json_cache.rb

@@ -71,7 +71,21 @@ module Gitlab
     end
 
     def parse_entry(raw, klass)
-      klass.new(raw) if valid_entry?(raw, klass)
+      return unless valid_entry?(raw, klass)
+      return klass.new(raw) unless klass.ancestors.include?(ActiveRecord::Base)
+
+      # When the cached value is a persisted instance of ActiveRecord::Base in
+      # some cases a relation can return an empty collection becauses scope.none!
+      # is being applied on ActiveRecord::Associations::CollectionAssociation#scope
+      # when the new_record? method incorrectly returns false.
+      #
+      # See https://gitlab.com/gitlab-org/gitlab-ee/issues/9903#note_145329964
+      attributes = klass.attributes_builder.build_from_database(raw, {})
+      klass.allocate.init_with("attributes" => attributes, "new_record" => new_record?(raw, klass))
+    end
+
+    def new_record?(raw, klass)
+      raw.fetch(klass.primary_key, nil).blank?
     end
 
     def valid_entry?(raw, klass)

spec/lib/gitlab/json_cache_spec.rb

@@ -297,13 +297,39 @@ describe Gitlab::JsonCache do
           expect(result).to eq(broadcast_message)
         end
 
+        context 'when the cached value is an instance of ActiveRecord::Base' do
+          it 'returns a persisted record when id is set' do
+            backend.write(expanded_key, broadcast_message.to_json)
+
+            result = cache.fetch(key, as: BroadcastMessage) { 'block result' }
+
+            expect(result).to be_persisted
+          end
+
+          it 'returns a new record when id is nil' do
+            backend.write(expanded_key, build(:broadcast_message).to_json)
+
+            result = cache.fetch(key, as: BroadcastMessage) { 'block result' }
+
+            expect(result).to be_new_record
+          end
+
+          it 'returns a new record when id is missing' do
+            backend.write(expanded_key, build(:broadcast_message).attributes.except('id').to_json)
+
+            result = cache.fetch(key, as: BroadcastMessage) { 'block result' }
+
+            expect(result).to be_new_record
+          end
+        end
+
         it "returns the result of the block when 'as' option is nil" do
           result = cache.fetch(key, as: nil) { 'block result' }
 
           expect(result).to eq('block result')
         end
 
-        it "returns the result of the block when 'as' option is not informed" do
+        it "returns the result of the block when 'as' option is missing" do
           result = cache.fetch(key) { 'block result' }
 
           expect(result).to eq('block result')