When using EntityManager.Instantiate, how does it replace child Entity references in IComponentData automatically?

Questions & Answers
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1

I have child Entity references stored in an IComponentData, if I instantiate this, how does it know to replace those references with instantiated ones automatically?

Does it only change fields of the type Entity? How about nested structs inside IComponentData…

2

When using EntityManager.Instantiate, how does it replace child Entity references in IComponentData automatically?

EntityManager.Instantiate is calling EntityRemapUtility from EntityComponentStoreCreateDestroyEntities.cs.

public static Entity RemapEntityForPrefab(Entity* remapSrc, Entity* remapDst, int remappingCount, Entity source)
{
    // When instantiating prefabs,
    // internal references are remapped.
    for (int i = 0; i != remappingCount; i++)
    {
        if (source == remapSrc*)
            _return remapDst*;
    }
    // And external references are kept.
    return source;
}

Does it only change fields of the type “Entity”?

Yes. EntityRemapUtility accepts Entity* value types.

If you have reasons to avoid this, you can smuggle an Entity value, for example, in an int2 field

public struct MyComponentData : IComponentData
{
    public int2 entityPtr;
}
 
comp.entityPtr = new int2{ x=someEntity.Index, y=someEntity.Version };
Entity recreated = new Entity{ Index=comp.entityPtr.x , Version=comp.entityPtr.y };