get relation by index

src/EntityComponentReader.cs

@@ -78,6 +78,12 @@ namespace MoonTools.ECS
 			return RelationDepot.OutRelationSingleton<TRelationKind>(entity.ID);
 		}
 
+		// NOTE: this WILL crash if at least n + 1 relations do not exist!
+		protected Entity NthOutRelation<TRelationKind>(in Entity entity, int n) where TRelationKind : unmanaged
+		{
+			return RelationDepot.NthOutRelation<TRelationKind>(entity.ID, n);
+		}
+
 		protected bool HasOutRelation<TRelationKind>(in Entity entity) where TRelationKind : unmanaged
 		{
 			return RelationDepot.HasOutRelation<TRelationKind>(entity.ID);
@@ -99,6 +105,12 @@ namespace MoonTools.ECS
 			return RelationDepot.InRelationSingleton<TRelationKind>(entity.ID);
 		}
 
+		// NOTE: this WILL crash if at least n + 1 relations do not exist!
+		protected Entity NthInRelation<TRelationKind>(in Entity entity, int n) where TRelationKind : unmanaged
+		{
+			return RelationDepot.NthInRelation<TRelationKind>(entity.ID, n);
+		}
+
 		protected bool HasInRelation<TRelationKind>(in Entity entity) where TRelationKind : unmanaged
 		{
 			return RelationDepot.HasInRelation<TRelationKind>(entity.ID);

src/RelationDepot.cs

@@ -76,6 +76,11 @@ namespace MoonTools.ECS
 			return Lookup<TRelationKind>().OutFirst(entityID);
 		}
 
+		public Entity NthOutRelation<TRelationKind>(int entityID, int n) where TRelationKind : unmanaged
+		{
+			return Lookup<TRelationKind>().OutNth(entityID, n);
+		}
+
 		public int OutRelationCount<TRelationKind>(int entityID) where TRelationKind : unmanaged
 		{
 			return Lookup<TRelationKind>().OutRelationCount(entityID);
@@ -91,6 +96,11 @@ namespace MoonTools.ECS
 			return Lookup<TRelationKind>().InRelations(entityID);
 		}
 
+		public Entity NthInRelation<TRelationKind>(int entityID, int n) where TRelationKind : unmanaged
+		{
+			return Lookup<TRelationKind>().InNth(entityID, n);
+		}
+
 		public Entity InRelationSingleton<TRelationKind>(int entityID) where TRelationKind : unmanaged
 		{
 			return Lookup<TRelationKind>().InFirst(entityID);

src/RelationStorage.cs

@@ -92,13 +92,18 @@ namespace MoonTools.ECS
 
 		public Entity OutFirst(int entityID)
 		{
+			return OutNth(entityID, 0);
+		}
+
+		public Entity OutNth(int entityID, int n)
+		{
 #if DEBUG
 			if (!outRelations.ContainsKey(entityID) || outRelations[entityID].Count == 0)
 			{
 				throw new KeyNotFoundException("No out relations to this entity!");
 			}
 #endif
-			return outRelations[entityID][0];
+			return outRelations[entityID][n];
 		}
 
 		public bool HasOutRelation(int entityID)
@@ -125,6 +130,11 @@ namespace MoonTools.ECS
 
 		public Entity InFirst(int entityID)
 		{
+			return InNth(entityID, 0);
+		}
+
+		public Entity InNth(int entityID, int n)
+		{
 #if DEBUG
 			if (!inRelations.ContainsKey(entityID) || inRelations[entityID].Count == 0)
 			{
@@ -132,7 +142,7 @@ namespace MoonTools.ECS
 			}
 #endif
 
-			return inRelations[entityID][0];
+			return inRelations[entityID][n];
 		}
 
 		public bool HasInRelation(int entityID)