check for specific relation

src/EntityComponentReader.cs

@@ -62,6 +62,11 @@ public abstract class EntityComponentReader
 		return RelationDepot.Relations<TRelationKind>();
 	}
 
+	protected bool Related<TRelationKind>(in Entity a, in Entity b)
+	{
+		return RelationDepot.Related<TRelationKind>(a.ID, b.ID);
+	}
+
 	protected IEnumerable<Entity> RelatedToA<TRelationKind>(in Entity entity)
 	{
 		return RelationDepot.RelatedToA<TRelationKind>(entity.ID);

src/RelationDepot.cs

@@ -37,6 +37,11 @@ namespace MoonTools.ECS
 			return Lookup<TRelationKind>().All();
 		}
 
+		public bool Related<TRelationKind>(int idA, int idB)
+		{
+			return Lookup<TRelationKind>().Has(new Relation(idA, idB));
+		}
+
 		public IEnumerable<Entity> RelatedToA<TRelationKind>(int entityID)
 		{
 			return Lookup<TRelationKind>().RelatedToA(entityID);

src/RelationStorage.cs

@@ -18,6 +18,7 @@ namespace MoonTools.ECS
 		public void Add(Relation relation)
 		{
 			if (relations.Contains(relation)) { return; }
+
 			var idA = relation.A.ID;
 			var idB = relation.B.ID;
 
@@ -36,6 +37,11 @@ namespace MoonTools.ECS
 			relations.Add(relation);
 		}
 
+		public bool Has(Relation relation)
+		{
+			return relations.Contains(relation);
+		}
+
 		public IEnumerable<Entity> RelatedToA(int entityID)
 		{
 			if (entitiesRelatedToA.ContainsKey(entityID))