docs: add note for GIST index on 'path' column in MyEntity and fix MyEntityListener preUpdate event handling

Author: landure

docs/LTREE-TYPE.md

@@ -39,7 +39,6 @@ use Symfony\Bridge\Doctrine\Types\UuidType;
 use Symfony\Component\Uid\Uuid;
 
 #[ORM\Entity()]
-#[ORM\Index(columns: ['path'])]
 #[ORM\EntityListeners([MyEntityListener::class])]
 class MyEntity implements \Stringable
 {
@@ -135,6 +134,16 @@ class MyEntity implements \Stringable
 }
 ```
 
+🗃️ Doctrine can't create [PostgreSQL GiST indexes](https://www.postgresql.org/docs/current/gist.html).
+Add a GiST index to an `ltree` column by manually adding its `CREATE INDEX`
+command to the migration:
+
+```sql
+// Example GiST index for ltree with a custom signature length (must be a multiple of 4)
+CREATE INDEX my_entity_path_gist_idx
+    ON my_entity USING GIST (path gist_ltree_ops(siglen = 100));
+```
+
 ⚠️ **Important**: Changing an entity's parent requires to cascade the change
 to all its children.
 This is not handled automatically by Doctrine.
@@ -150,17 +159,24 @@ when the `path` is present in the changed fields:
 namespace App\EventListener;
 
 use App\Entity\MyEntity;
+use Doctrine\Bundle\DoctrineBundle\Attribute\AsEntityListener;
 use Doctrine\ORM\Event\PreUpdateEventArgs;
-use Doctrine\ORM\Mapping as ORM;
+use Doctrine\ORM\Events;
 
+#[AsEntityListener(event: Events::preUpdate, method: 'preUpdate', entity: MyEntity::class)]
 final readonly class MyEntityListener
 {
-    #[ORM\PreUpdate]
     public function preUpdate(MyEntity $entity, PreUpdateEventArgs $eventArgs): void
     {
         if ($eventArgs->hasChangedField('path')) {
+            $em  = $eventArgs->getObjectManager();
+            $uow = $em->getUnitOfWork();
+            $meta = $em->getClassMetadata(MyEntity::class);
+
             foreach($entity->getChildren() as $child) {
                 $child->setParent($entity);
+                // Ensure Doctrine picks up the modification
+                $uow->recomputeSingleEntityChangeSet($meta, $child);
             }
         }
     }