implement multi relation loading

src/PersistentData/Model/Model.php

@@ -8,6 +8,8 @@ abstract class Model
 
     protected static array $relations = [];
 
+    protected static array $multiRelations = [];
+
     protected $id = null;
 
     private array $snapshot = [];
@@ -27,6 +29,11 @@ abstract class Model
         return static::$relations;
     }
 
+    public static function getMultiRelations(): array
+    {
+        return static::$multiRelations;
+    }
+
     public function setId($id): void
     {
         $this->id = $id;