Currently this mapping will fail:

public record BookProjection(@IdProjection id, @ObjectProjection AuthorDTO author) {};
public record BookProjection(@IdProjection id, @FieldProjection name) {};

… because the @IdProjection is not allowed within an object projection.

That makes sense, because @IdProjection is about the root document ID. But it’s not very intuitive.

Maybe we could extend the ID projection to allow referring to object IDs as well?