@Override
  public int hashCode() {
    return Objects.hash(key, samzaSqlRelRecord);
  }
Creates the SamzaSqlRelMessage from {@link SamzaSqlRelRecord}.
@param samzaSqlRelRecord represents the rel record.
@param metadata the message/event's metadata
samza-sql/src/main/java/org/apache/samza/sql/data/SamzaSqlRelMessage.java