Merge pull request #70 from clio/fix_poly_n_plus_one_false_alarm

Fix polymorphic assocation with nil type N+1 false alarm issue

lib/jit_preloader/active_record/associations/singular_association.rb

@@ -18,13 +18,17 @@ def load_target
           # always an N+1 query.
           record.jit_n_plus_one_tracking ||= owner.jit_n_plus_one_tracking if record
 
-          if !jit_loaded && owner.jit_n_plus_one_tracking
+          if !jit_loaded && owner.jit_n_plus_one_tracking && !is_polymorphic_association_without_type
             ActiveSupport::Notifications.publish("n_plus_one_query",
                                                  source: owner, association: reflection.name)
           end
         end
       end
     end
+
+    private def is_polymorphic_association_without_type
+      self.is_a?(ActiveRecord::Associations::BelongsToPolymorphicAssociation) && self.klass.nil?
+    end
   end
 end
 

spec/lib/jit_preloader/preloader_spec.rb

@@ -171,9 +171,13 @@
           contact1.update!(contact_owner_type: nil, contact_owner_id: nil)
         end
 
-        it "successfully load the rest of association values" do
+        it "successfully load the rest of association values and does not publish a n+1 notification" do
           contacts = Contact.jit_preload.to_a
-          expect(contacts.first.contact_owner).to eq(nil)
+          ActiveSupport::Notifications.subscribed(callback, "n_plus_one_query") do
+            expect(contacts.first.contact_owner).to eq(nil)
+          end
+
+          expect(source_map).to eql({})
 
           expect do
             contacts.first.contact_owner
@@ -184,17 +188,6 @@
           expect(contacts.second.contact_owner).to eq(ContactOwner.first)
           expect(contacts.third.contact_owner).to eq(Address.first)
         end
-
-        it "publish N+1 notification due to polymorphic nil type" do
-          contacts = Contact.jit_preload.to_a
-
-          ActiveSupport::Notifications.subscribed(callback, "n_plus_one_query") do
-            contacts.first.contact_owner
-          end
-
-          expect_source_map = { contacts.first => [:contact_owner] }
-          expect(source_map).to eql(expect_source_map)
-        end
       end
     end
   end