- Add EntityRelations<>

- replaced RelationExtensions.GetAllEntitiesWithRelations() -> EntityRelations<TRelation>().Entities
- replaced RelationExtensions.ForAllEntityRelations()       -> EntityRelations<TRelation>().For()

src/ECS/Relations/EntityRelations.cs

@@ -0,0 +1,37 @@
+using Friflo.Engine.ECS.Relations;
+
+// ReSharper disable once CheckNamespace
+namespace Friflo.Engine.ECS;
+
+public readonly struct EntityRelations <TRelation>
+    where TRelation : struct, IRelation
+{
+    private readonly AbstractEntityRelations relations;
+
+    internal EntityRelations(AbstractEntityRelations relations) {
+        this.relations = relations;
+    }
+
+    /// <summary>
+    /// Returns a collection of entities having one or more relations of the specified <typeparamref name="TRelation"/> type.<br/>
+    /// Executes in O(1).
+    /// </summary>
+    /// <remarks>
+    /// <list type="bullet">
+    ///   <item>
+    ///     The returned collection changes when relations are updated, removed or added.
+    ///   </item>
+    ///   <item>
+    ///     To get all entities including their relations (the cartesian product aka CROSS JOIN) use<br/>
+    ///     <see cref="RelationExtensions.GetAllEntityRelations{TRelation}"/>
+    ///   </item>
+    /// </list>
+    /// </remarks>
+    public EntityReadOnlyCollection Entities => new EntityReadOnlyCollection(relations.store, relations.positionMap.Keys);
+
+    /// <summary>
+    /// Iterates all entity relations of the specified <typeparamref name="TRelation"/> type.<br/>
+    /// Executes in O(N) N: number of all entity relations.
+    /// </summary>
+    public void For(ForEachEntity<TRelation> lambda) => relations.ForAllEntityRelations(lambda);
+}

src/ECS/Relations/RelationExtensions.cs

@@ -3,7 +3,6 @@
 
 using System;
 using System.Collections.Generic;
-using System.Diagnostics.CodeAnalysis;
 using Friflo.Engine.ECS.Relations;
 
 // ReSharper disable once CheckNamespace
@@ -103,7 +102,15 @@ public static EntityLinks<TRelation> GetIncomingLinks<TRelation>(this Entity tar
     #endregion
 
 #region EntityStore
+    public static EntityRelations<TRelation> EntityRelations<TRelation>(this EntityStore store)
+        where TRelation : struct, IRelation
+    {
+        var relations = AbstractEntityRelations.GetEntityRelations(store, StructInfo<TRelation>.Index);
+        return new EntityRelations<TRelation>(relations);
+    }
+
     /// <summary>
+    /// Obsolete: Use <see cref="EntityRelations{TRelation}.Entities"/><br/>
     /// Returns a collection of entities having one or more relations of the specified <typeparamref name="TRelation"/> type.<br/>
     /// Executes in O(1).
     /// </summary>
@@ -118,6 +125,7 @@ public static EntityLinks<TRelation> GetIncomingLinks<TRelation>(this Entity tar
     ///   </item>
     /// </list>
     /// </remarks>
+    [Obsolete("replace with property: EntityRelations<TRelation>().Entities")]
     public static EntityReadOnlyCollection GetAllEntitiesWithRelations<TRelation>(this EntityStore store)
         where TRelation : struct, IRelation
     {
@@ -126,9 +134,11 @@ public static EntityReadOnlyCollection GetAllEntitiesWithRelations<TRelation>(th
     }
 
     /// <summary>
+    /// Obsolete: Use <see cref="EntityRelations{TRelation}.For"/><br/>
     /// Iterates all entity relations of the specified <typeparamref name="TRelation"/> type.<br/>
     /// Executes in O(N) N: number of all entity relations.
     /// </summary>
+    [Obsolete("replace with method: EntityRelations<TRelation>().For()")]
     public static void ForAllEntityRelations<TRelation>(this EntityStore store, ForEachEntity<TRelation> lambda)
         where TRelation : struct, IRelation
     {
@@ -146,12 +156,5 @@ public static (Entities entities, Chunk<TRelation> relations) GetAllEntityRelati
         var entityRelations = AbstractEntityRelations.GetEntityRelations(store, StructInfo<TRelation>.Index);
         return entityRelations.GetAllEntityRelations<TRelation>();
     }
-
-    [ExcludeFromCodeCoverage]
-    public static IReadOnlyCollection<Entity> GetAllLinkedEntities<TRelation>(this EntityStore store)
-        where TRelation: struct, IRelation
-    {
-        throw new NotImplementedException();
-    }
     #endregion
 }

src/Tests/ECS/Relations/Test_Relations.cs

@@ -227,7 +227,7 @@ public static void Test_Relations_Enumerator()
     public static void Test_Relations_EntityReadOnlyCollection()
     {
         var store   = new EntityStore();
-        var entities = store.GetAllEntitiesWithRelations<IntRelation>();
+        var entities = store.EntityRelations<IntRelation>().Entities;
 
         var entity1 = store.CreateEntity(1);
         var entity2 = store.CreateEntity(2);

src/Tests/ECS/Relations/Test_Relations_Delete.cs

@@ -12,7 +12,7 @@ public static class Test_Relations_Delete
     public static void Test_Relations_Delete_int_relations()
     {
         var store       = new EntityStore();
-        var allEntities = store.GetAllEntitiesWithRelations<IntRelation>();
+        var allEntities = store.EntityRelations<IntRelation>().Entities;
         AreEqual("{ }",         allEntities.Debug());
 
         var entity1 = store.CreateEntity(1);
@@ -29,7 +29,7 @@ public static void Test_Relations_Delete_int_relations()
 
         int count = 0;
         // --- version: iterate all entity relations in O(N)
-        store.ForAllEntityRelations((ref IntRelation relation, Entity entity) => {
+        store.EntityRelations<IntRelation>().For((ref IntRelation relation, Entity entity) => {
             switch (count++) {
                 case 0: AreEqual(1, entity.Id); AreEqual(10, relation.value); break;
                 case 1: AreEqual(1, entity.Id); AreEqual(20, relation.value); break;
@@ -54,7 +54,7 @@ public static void Test_Relations_Delete_int_relations()
     public static void Test_Relations_Delete_Entity_relations()
     {
         var store       = new EntityStore();
-        var sourceNodes = store.GetAllEntitiesWithRelations<AttackRelation>();
+        var sourceNodes = store.EntityRelations<AttackRelation>().Entities;
         AreEqual("{ }",         sourceNodes.Debug());
 
         var target10    = store.CreateEntity(10);
@@ -76,7 +76,7 @@ public static void Test_Relations_Delete_Entity_relations()
 
         int count = 0;
         // --- version: iterate all entity relations in O(N)
-        store.ForAllEntityRelations((ref AttackRelation relation, Entity entity) => {
+        store.EntityRelations<AttackRelation>().For((ref AttackRelation relation, Entity entity) => {
             switch (count++) {
                 case 0: AreEqual(1, entity.Id); AreEqual(10, relation.target.Id); break;
                 case 1: AreEqual(1, entity.Id); AreEqual(11, relation.target.Id); break;

src/Tests/ECS/Relations/Test_Relations_Query.cs

@@ -197,7 +197,7 @@ public static void Test_Relations_ForAllEntityRelations_Perf()
         int count = 0;
         var sw = new Stopwatch();
         sw.Start();
-        store.ForAllEntityRelations((ref IntRelation relation, Entity entity) => {
+        store.EntityRelations<IntRelation>().For((ref IntRelation relation, Entity entity) => {
             count++;
         });
         AreEqual(entityCount * relationsPerEntity, count);