Utility Features

Entity References

In some cases, you may want to reference entities among themselves. Instead of an Entity you should refer to an EntityReference instead. This references an entity and also stores a version to check if the original entity still exists.

using var world = World.Create();

var entity = world.Create(_entityGroup);
var reference = world.Reference(entity);  // This should be stored in your component ( entity.Reference() is also available. )

// Checks if the entity is the same as before by comparing the version and its id
if(reference.IsAlive()) {
    var cmps = reference.Entity.Get(...);
}     

Command Buffers

Entity creation, deletion, and structural changes can happen during a query or entity iteration.
Sometimes, however, it makes sense to record operations and later transfer them to the world.
For this reason, command buffers exist.

var entity = world.Create<Transform, Rotation, int>();                                                               // Entity in world.
var bufferedEntity = commandBuffer.Create(new ComponentType[] {typeof(Transform), typeof(Rotation), typeof(int) });  // Later also generic overloads to get rid of arrays. 
        
// Records operations on the existing entity.
commandBuffer.Set(in entity, new Transform{ X = 20, Y = 20});
commandBuffer.Add(in entity, new Ai());
        
// Records operations on the buffered entity. 
commandBuffer.Set(in bufferedEntity, new Transform{ X = 20, Y = 20});
commandBuffer.Add(in bufferedEntity, new Ai());

// Transfers them into the world. 
commandBuffer.Playback();

Buffers are threadsafe and very fast, perfect for such scenarios. They can and should always be reused! :)