+ deletion rules

samples/MyBattleground/Program.cs

@@ -8,6 +8,10 @@
 
 using var ecs = new World();
 
+
+var asd = ecs.Entity().Set(new Position());
+var name = ecs.Entity<Position>().Name();
+
 ecs.Query<Optional<Position>>();
 ecs.Query<(Position, Velocity), (With<Networked>, Without<Likes>, Or<(With<Position>, Without<ManagedData>)>)>();
 
@@ -21,16 +25,15 @@
 var root = ecs.Entity();
 var child = ecs.Entity();
 
-var child2 = ecs.Entity();
-child2.Set(root, child);
-
-if (child2.Has(root, child))
-{
 
-}
+var eqiupId = ecs.Entity<EquippedItem>().Add<Defaults.OnDelete, Defaults.Unset>();
 
-child.Add<EquippedItem>(root);
 child.Set(new EquippedItem() { Layer = 3 }, root);
+child.Set(new EquippedItem() { Layer = 3 }, root);
+
+// root.AddChild(child);
+root.Delete();
+
 ref var equip2 = ref ecs.Get<EquippedItem>(child);
 ref var equip = ref ecs.Get<EquippedItem>(child, root);
 equip.Layer = 8;

src/Default.cs

@@ -78,4 +78,70 @@ public struct Symmetric { }
 	/// </example>
     /// </summary>
 	public struct DoNotDelete { }
+
+	/// <summary>
+    /// Built-in tag.<br/>Cleanup rule<para/>
+	/// <example>
+	/// 	Example:
+	/// <code>
+	/// 	var a = world.Entity();
+	///		var relation = world.Entity().Add&lt;OnDelete, Delete&gt;();
+	///		var b = world.Entity();
+	///
+	///		a.Add(relation, b);
+	///		b.Delete(); // --> a get deleted too
+	/// </code>
+	/// </example>
+    /// </summary>
+	public struct OnDelete { }
+
+
+	/// <summary>
+    /// Built-in tag.<br/>Cleanup rule for Delete<para/>
+	/// <example>
+	/// 	Example:
+	/// <code>
+	/// 	var a = world.Entity();
+	///		var relation = world.Entity().Add&lt;OnDelete, Delete&gt;();
+	///		var b = world.Entity();
+	///
+	///		a.Add(relation, b);
+	///		b.Delete(); // --> 'a' get deleted too
+	/// </code>
+	/// </example>
+    /// </summary>
+	public struct Delete { }
+
+	/// <summary>
+    /// Built-in tag.<br/>Cleanup rule for Delete<para/>
+	/// <example>
+	/// 	Example:
+	/// <code>
+	/// 	var a = world.Entity();
+	///		var relation = world.Entity().Add&lt;OnDelete, Panic&gt;();
+	///		var b = world.Entity();
+	///
+	///		a.Add(relation, b);
+	///		b.Delete(); // --> runtime error!
+	/// </code>
+	/// </example>
+    /// </summary>
+	public struct Panic { }
+
+
+	/// <summary>
+    /// Built-in tag.<br/>Cleanup rule for Delete<para/>
+	/// <example>
+	/// 	Example:
+	/// <code>
+	/// 	var a = world.Entity();
+	///		var relation = world.Entity().Add&lt;OnDelete, Unset&gt;();
+	///		var b = world.Entity();
+	///
+	///		a.Add(relation, b);
+	///		b.Delete(); // --> relation get removed from 'a'
+	/// </code>
+	/// </example>
+    /// </summary>
+	public struct Unset { }
 }

src/World.Public.cs

@@ -34,14 +34,25 @@ public World(ulong maxComponentId = 256)
 		_ = Component<Name>();
 		_ = Component<ChildOf>();
 
+		_ = Component<OnDelete>();
+		_ = Component<Delete>();
+		_ = Component<Panic>();
+		_ = Component<Unset>();
+
 		setCommon(Entity<DoNotDelete>(), nameof(DoNotDelete));
 		setCommon(Entity<Unique>(), nameof(Unique));
 		setCommon(Entity<Symmetric>(), nameof(Symmetric));
 		setCommon(Entity<Wildcard>(), nameof(Wildcard));
 		setCommon(Entity<Identifier>(), nameof(Identifier));
 		setCommon(Entity<Name>(), nameof(Name));
 		setCommon(Entity<ChildOf>(), nameof(ChildOf))
+			.Add<OnDelete, Delete>()
+			.Add<Unique>();
+		setCommon(Entity<OnDelete>(), nameof(OnDelete))
 			.Add<Unique>();
+		setCommon(Entity<Delete>(), nameof(Delete));
+		setCommon(Entity<Panic>(), nameof(Panic));
+		setCommon(Entity<Unset>(), nameof(Unset));
 
 		static EntityView setCommon(EntityView entity, string name)
 			=> entity.Add<DoNotDelete>().Set<Identifier, Name>(new (name));
@@ -208,11 +219,20 @@ public void Delete(EcsID entity)
 			// 		 https://github.com/SanderMertens/flecs/blob/master/include/flecs/private/api_defines.h#L289
 			var term0 = new QueryTerm(IDOp.Pair(Wildcard.ID, entity), TermOp.With);
 			var term1 = new QueryTerm(IDOp.Pair(entity, Wildcard.ID), TermOp.With);
-			QueryRaw(term0).Each(static (EntityView child) => child.Delete());
-			QueryRaw(term1).Each(static (EntityView child) => child.Delete());
 
-			ref var record = ref GetRecord(entity);
+			QueryFilterDelegateWithEntity onQuery = (EntityView child) => {
+				var action = Action(child.ID, entity);
+				if (Has<OnDelete, Delete>(action))
+					child.Delete();
+				if (Has<OnDelete, Unset>(action))
+					child.Unset(action, entity);
+				if (Has<OnDelete, Panic>(action))
+					EcsAssert.Panic(false, "you cant remove this entity because of {OnDelete, Panic} relation");
+			};
+			QueryRaw(term0).Each(onQuery);
+			QueryRaw(term1).Each(onQuery);
 
+			ref var record = ref GetRecord(entity);
 			var removedId = record.Archetype.Remove(ref record);
 			EcsAssert.Assert(removedId == entity);
 

tests/Relation.cs

@@ -263,5 +263,50 @@ public void Relation_SymmetricDeferred()
 			Assert.True(carl.Has(tradeWith, bob));
 			Assert.True(bob.Has(tradeWith, carl));
 		}
+
+		[Fact]
+		public void Relation_OnDelete_Delete()
+		{
+			using var ctx = new Context();
+
+			var a = ctx.World.Entity();
+			var relation = ctx.World.Entity().Add<OnDelete, Delete>();
+			var b = ctx.World.Entity();
+
+			a.Add(relation, b);
+			b.Delete();
+
+			Assert.False(a.Exists());
+			Assert.False(b.Exists());
+		}
+
+		[Fact]
+		public void Relation_OnDelete_Unset()
+		{
+			using var ctx = new Context();
+
+			var a = ctx.World.Entity();
+			var relation = ctx.World.Entity().Add<OnDelete, Unset>();
+			var b = ctx.World.Entity();
+
+			a.Add(relation, b);
+			b.Delete();
+
+			Assert.True(a.Exists());
+			Assert.False(a.Has(relation, b));
+		}
+
+		[Fact]
+		public void Relation_OnDelete_Panic()
+		{
+			using var ctx = new Context();
+
+			var a = ctx.World.Entity();
+			var relation = ctx.World.Entity().Add<OnDelete, Panic>();
+			var b = ctx.World.Entity();
+
+			a.Add(relation, b);
+			Assert.ThrowsAny<Exception>(() => b.Delete());
+		}
     }
 }