clazz_ attribute in hibernate query

Question

In Hibernate table per concrete class strategy when fetched with super class following query is generated:

SELECT vehicle0_.VEHICLE_ID    AS VEHICLE_ID1_2_,
  vehicle0_.MANUFACTURER       AS MANUFACTURER2_2_,
  vehicle0_.PASSENGER_CAPACITY AS PASSENGER_CAPACITY1_0_,
  vehicle0_.LOAD_CAPACITY      AS LOAD_CAPACITY1_1_,
  vehicle0_.clazz_             AS clazz_
FROM
  (SELECT VEHICLE_ID,
    MANUFACTURER,
    PASSENGER_CAPACITY,
    NULL AS LOAD_CAPACITY,
    1    AS clazz_
  FROM PassengerVehicle
  UNION ALL
  SELECT VEHICLE_ID,
    MANUFACTURER,
    NULL AS PASSENGER_CAPACITY,
    LOAD_CAPACITY,
    2 AS clazz_
  FROM TransportationVehicle
  ) vehicle0_

vehicle0_.clazz_ is selected in query which is not there in table nor in class, what is this clazz_ attribute?

Answer 1

That's inheritance discriminator.

When you joined your subclass with super class, do avoid the confusion while instantiating from the result set, hibernate internally uses the column 'clazz'.