From 52fb5371406b50e60e46e96b8a72107c45e413dd Mon Sep 17 00:00:00 2001
From: Ullrich Praetz <ullrich@praetz.de>
Date: Mon, 11 Nov 2024 08:38:15 +0100
Subject: [PATCH] Fix: clear parent when deleting an entity used as a child.
 See: https://github.com/friflo/Friflo.Engine.ECS/issues/29

---
 src/ECS/Entity/Store/NodeTree.cs         |  1 +
 src/Tests/ECS/Entity/Test_Entity_Tree.cs | 17 +++++++++++++++++
 2 files changed, 18 insertions(+)

diff --git a/src/ECS/Entity/Store/NodeTree.cs b/src/ECS/Entity/Store/NodeTree.cs
index b5f52897..8d28a0f1 100644
--- a/src/ECS/Entity/Store/NodeTree.cs
+++ b/src/ECS/Entity/Store/NodeTree.cs
@@ -539,6 +539,7 @@ internal void DeleteNode(Entity entity)
         if (!HasParent(parentId)) {
             return;
         }
+        RemoveTreeParent(id);
         int curIndex = RemoveChildNode(parentId, id);
         OnChildNodeRemove(parentId, id, curIndex);
     }
diff --git a/src/Tests/ECS/Entity/Test_Entity_Tree.cs b/src/Tests/ECS/Entity/Test_Entity_Tree.cs
index 359b2119..bde5c2a3 100644
--- a/src/Tests/ECS/Entity/Test_Entity_Tree.cs
+++ b/src/Tests/ECS/Entity/Test_Entity_Tree.cs
@@ -768,6 +768,23 @@ public static void Test_Entity_Tree_ChildEnumerator()
         }
     }
     
+    // https://github.com/friflo/Friflo.Engine.ECS/issues/29
+    [Test]
+    public static void Test_Entity_Tree_CreateThenDestroyEntityWithParent()
+    {
+        var store = new EntityStore();
+        var root  = store.CreateEntity();
+        var child1 = store.CreateEntity();
+        root.AddChild(child1);
+        int id = child1.Id;
+        var parent = child1.Parent;
+
+        child1.DeleteEntity();
+        var child2 = store.CreateEntity();
+        IsTrue(child2.Parent.IsNull);   // before fix this assertion failed
+        AreEqual(id, child2.Id);        // uses recycled id
+    }
+    
     [Test]
     public static void Test_Entity_Tree_id_argument_exceptions()
     {