move the getEntityManager, only get it if needed

Author: OskarStark

cookbook/doctrine/event_listeners_subscribers.rst

@@ -135,10 +135,10 @@ a ``postPersist`` method, which will be called when the event is dispatched::
         public function postPersist(LifecycleEventArgs $args)
         {
             $entity = $args->getEntity();
-            $entityManager = $args->getEntityManager();
 
             // perhaps you only want to act on some "Product" entity
             if ($entity instanceof Product) {
+                $entityManager = $args->getEntityManager();
                 // ... do something with the Product
             }
         }
@@ -191,10 +191,10 @@ interface and have an event method for each event it subscribes to::
         public function index(LifecycleEventArgs $args)
         {
             $entity = $args->getEntity();
-            $entityManager = $args->getEntityManager();
 
             // perhaps you only want to act on some "Product" entity
             if ($entity instanceof Product) {
+                $entityManager = $args->getEntityManager();
                 // ... do something with the Product
             }
         }