func (gc *GarbageCollector) patchObject(item objectReference, patch []byte) (*runtime.Unstructured, error) {
	fqKind := unversioned.FromAPIVersionAndKind(item.APIVersion, item.Kind)
	client, err := gc.clientPool.ClientForGroupVersion(fqKind.GroupVersion())
	resource, err := gc.apiResource(item.APIVersion, item.Kind, len(item.Namespace) != 0)
	if err != nil {
		return nil, err
	}
	return client.Resource(resource, item.Namespace).Patch(item.Name, api.StrategicMergePatchType, patch)
}

func (gc *GarbageCollector) updateObject(item objectReference, obj *runtime.Unstructured) (*runtime.Unstructured, error) {
	fqKind := unversioned.FromAPIVersionAndKind(item.APIVersion, item.Kind)
	client, err := gc.clientPool.ClientForGroupVersion(fqKind.GroupVersion())
	resource, err := gc.apiResource(item.APIVersion, item.Kind, len(item.Namespace) != 0)
	if err != nil {
		return nil, err
	}
	return client.Resource(resource, item.Namespace).Update(obj)
}

func (gc *GarbageCollector) getObject(item objectReference) (*runtime.Unstructured, error) {
	fqKind := unversioned.FromAPIVersionAndKind(item.APIVersion, item.Kind)
	client, err := gc.clientPool.ClientForGroupVersion(fqKind.GroupVersion())
	gc.registeredRateLimiter.registerIfNotPresent(fqKind.GroupVersion(), client, "garbage_collector_operation")
	resource, err := gc.apiResource(item.APIVersion, item.Kind, len(item.Namespace) != 0)
	if err != nil {
		return nil, err
	}
	return client.Resource(resource, item.Namespace).Get(item.Name)
}

func (gc *GarbageCollector) deleteObject(item objectReference) error {
	fqKind := unversioned.FromAPIVersionAndKind(item.APIVersion, item.Kind)
	client, err := gc.clientPool.ClientForGroupVersion(fqKind.GroupVersion())
	resource, err := gc.apiResource(item.APIVersion, item.Kind, len(item.Namespace) != 0)
	if err != nil {
		return err
	}
	uid := item.UID
	preconditions := v1.Preconditions{UID: &uid}
	deleteOptions := v1.DeleteOptions{Preconditions: &preconditions}
	return client.Resource(resource, item.Namespace).Delete(item.Name, &deleteOptions)
}

// apiResource consults the REST mapper to translate an <apiVersion, kind,
// namespace> tuple to a unversioned.APIResource struct.
func (gc *GarbageCollector) apiResource(apiVersion, kind string, namespaced bool) (*unversioned.APIResource, error) {
	fqKind := unversioned.FromAPIVersionAndKind(apiVersion, kind)
	mapping, err := gc.restMapper.RESTMapping(fqKind.GroupKind(), apiVersion)
	if err != nil {
		return nil, fmt.Errorf("unable to get REST mapping for kind: %s, version: %s", kind, apiVersion)
	}
	glog.V(6).Infof("map kind %s, version %s to resource %s", kind, apiVersion, mapping.Resource)
	resource := unversioned.APIResource{
		Name:       mapping.Resource,
		Namespaced: namespaced,
		Kind:       kind,
	}
	return &resource, nil
}

func (obj *ExternalType2) GroupVersionKind() *unversioned.GroupVersionKind {
	return unversioned.FromAPIVersionAndKind(obj.APIVersion, obj.Kind)
}

func (gc *GarbageCollector) processItem(item *node) error {
	// Get the latest item from the API server
	latest, err := gc.getObject(item.identity)
	if err != nil {
		if errors.IsNotFound(err) {
			// the Propagator can add "virtual" node for an owner that doesn't
			// exist yet, so we need to enqueue a virtual Delete event to remove
			// the virtual node from Propagator.uidToNode.
			glog.V(6).Infof("item %v not found, generating a virtual delete event", item.identity)
			event := event{
				eventType: deleteEvent,
				obj:       objectReferenceToUnstructured(item.identity),
			}
			gc.propagator.eventQueue.Add(event)
			return nil
		}
		return err
	}
	if latest.GetUID() != item.identity.UID {
		glog.V(6).Infof("UID doesn't match, item %v not found, ignore it", item.identity)
		return nil
	}
	ownerReferences := latest.GetOwnerReferences()
	if len(ownerReferences) == 0 {
		glog.V(6).Infof("object %s's doesn't have an owner, continue on next item", item.identity)
		return nil
	}
	// TODO: we need to remove dangling references if the object is not to be
	// deleted.
	for _, reference := range ownerReferences {
		// TODO: we need to verify the reference resource is supported by the
		// system. If it's not a valid resource, the garbage collector should i)
		// ignore the reference when decide if the object should be deleted, and
		// ii) should update the object to remove such references. This is to
		// prevent objects having references to an old resource from being
		// deleted during a cluster upgrade.
		fqKind := unversioned.FromAPIVersionAndKind(reference.APIVersion, reference.Kind)
		client, err := gc.clientPool.ClientForGroupVersion(fqKind.GroupVersion())
		if err != nil {
			return err
		}
		resource, err := gc.apiResource(reference.APIVersion, reference.Kind, len(item.identity.Namespace) != 0)
		if err != nil {
			return err
		}
		owner, err := client.Resource(resource, item.identity.Namespace).Get(reference.Name)
		if err == nil {
			if owner.GetUID() != reference.UID {
				glog.V(6).Infof("object %s's owner %s/%s, %s is not found, UID mismatch", item.identity.UID, reference.APIVersion, reference.Kind, reference.Name)
				continue
			}
			glog.V(6).Infof("object %s has at least an existing owner, will not garbage collect", item.identity.UID)
			return nil
		} else if errors.IsNotFound(err) {
			glog.V(6).Infof("object %s's owner %s/%s, %s is not found", item.identity.UID, reference.APIVersion, reference.Kind, reference.Name)
		} else {
			return err
		}
	}
	glog.V(2).Infof("none of object %s's owners exist any more, will garbage collect it", item.identity)
	return gc.deleteObject(item.identity)
}

func (obj *MyAPIObject) GroupVersionKind() unversioned.GroupVersionKind {
	return unversioned.FromAPIVersionAndKind(obj.TypeMeta.APIVersion, obj.TypeMeta.Kind)
}

func (obj *MyWeirdCustomEmbeddedVersionKindField) GroupVersionKind() unversioned.GroupVersionKind {
	return unversioned.FromAPIVersionAndKind(obj.APIVersion, obj.ObjectKind)
}

func (obj *Config) GroupVersionKind() unversioned.GroupVersionKind {
	return unversioned.FromAPIVersionAndKind(obj.APIVersion, obj.Kind)
}

func (obj *ObjectReference) GroupVersionKind() unversioned.GroupVersionKind {
	return unversioned.FromAPIVersionAndKind(obj.APIVersion, obj.Kind)
}

// GroupVersionKind satisfies the ObjectKind interface for all objects that embed TypeMeta
func (obj *TypeMeta) GroupVersionKind() *unversioned.GroupVersionKind {
	return unversioned.FromAPIVersionAndKind(obj.APIVersion, obj.Kind)
}

func (obj *InternalObject) GroupVersionKind() *unversioned.GroupVersionKind {
	return unversioned.FromAPIVersionAndKind(obj.TypeMeta.APIVersion, obj.TypeMeta.Kind)
}