How to do inverse ComponentGroup filter and get all entities that does not match?

I am trying the `SerializeUtility` and the main problem is it must serialize the whole world. There is `EntityManager.MoveEntitiesFrom` to move ALL entities to my save world and then I want to make it so that only what I want remains meaning that I have to destroy everything else.

Currently only `entityManager.DestroyEntity(componentGroupFilter)` comes to mind but it destroy all matched entities. Any approach to make it the other way that the matched entities remains?

(Also I cannot GetComponentGroup of the save world via save world's entityManager alone? How to filter in other world while you are in default world's code?)

Code (CSharp):

1.         //We are in DefaultWorld's ComponentSystem code.
2.  
3.         World saveWorld = new World(nameof(saveWorld));
4.         var emSave = saveWorld.CreateManager<EntityManager>();
5.         emSave.MoveEntitiesFrom(EntityManager);
6.  
7.         emSave.DestroyEntity( ??? );
8.  
9.         SerializeUtility.SerializeWorld(emSave, binaryWriter, out _);

 

Can't you add a tag component to each "saveable" entity and use a subtractive component query? i.e. delete all entities that doesn't have that component?

EntityManager.DestroyEntity(GetComponentGroup(ComponentType.Subtractive<Saveable>()));