class ContentEntityBase {

  public function __sleep() {
    $deep_serialization = $this->deepSerialization;
    if ($this->isBeingSerialized) {
      $deep_serialization = FALSE;
    }

    $this->isBeingSerialized = TRUE;
    foreach (... as $field) {
      ... = $field->getSerializationValue($deep_serialization);
    }
    $this->isBeingSerialized = FALSE;
  }

}