Efficient way of deleting entities.

[sergiyha]

Hi. I have a question about deleting entities functionality. In my game, I must delete all entities from storage to fill it again after relogin. I use this pseudocode:

		var testStore = new EntityStore();

		testStore.CreateEntity();
		testStore.CreateEntity();
		testStore.CreateEntity();
		testStore.CreateEntity();
		testStore.CreateEntity();
		testStore.CreateEntity();

		var cb = testStore.GetCommandBuffer();
		foreach (var entity in testStore.Entities)
		{
			cb.DeleteEntity(entity.Id);
		}
		
		cb.Playback();

What bothers me is the description of Entities in storage. It says that "Property is mainly used for debugging". What kind of improvement can I apply in this case? Thanks!

[friflo]

Hi, in case you only want to delete entities the most efficient way currently is:

        var store = new EntityStore(PidType.UsePidAsId);
        for (int n = 0; n < 1000_000; n++) {
            store.CreateEntity();
        }
        var entities = new List<Entity>(store.Entities.Count);
        foreach (var entity in store.Entities) {
            entities.Add(entity);
        }
        foreach (var entity in entities) {
            entity.DeleteEntity();
        }

I guess will add an EntityStore.DeleteEntity(int id) in future which will be faster than entity.DeleteEntity().

[friflo]

The intention of the remarks "Property is mainly used for debugging" for EntityStore.Entities was
to avoid writing code like this.

        foreach (var entity in store.Entities) {
            ref var position = ref entity.GetComponent<Position>();
            ref var rotation = ref entity.GetComponent<Rotation>();
            ...
        }

instead of the much more performant way like.

        var query = store.Query<Position, Rotation>();
        query.ForEachEntity((ref Position position, ref Rotation rotation, Entity entity) => {
            ...
        });

[sergiyha]

Ah. Got it!