public class UserModel {

  [MongoIndex(IndexName = nameof(UserId), IndexType = IndexType.Ascending)]
  public System.Guid UserId {get;set;}

  [MongoIndex(IndexName = nameof(Firstname), IndexType = IndexType.Text)]
  public string Firstname {get;set;}

  [MongoIndex(IndexName = nameof(Surname), IndexType = IndexType.Text)]
  public string Surname {get;set;}

}