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?

score 2 · Accepted Answer · answered Sep 11 '15 at 06:46

2

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'.

answered Sep 11 '15 at 06:46

Suresh Atta

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I thought inheritance discriminator is needed when working with single table strategy, this column is added while working with joined and table_per_class strategy. In both of the strategy it does select from separate table then why this column is needed? – eatSleepCode Sep 11 '15 at 07:04
There are two more questions that are really putting me in confusion. It would be nice and helpful for me if you can answer those question. http://stackoverflow.com/questions/32516409/difference-hibernate-with-dialect-and-without-dialect and http://stackoverflow.com/questions/32472739/hibernate-merge-method-persists-the-copy-of-entity – eatSleepCode Sep 11 '15 at 07:07
@eatSleepCode It selects that is fine, but which subclass needs to instantiate with hibernate ? That's the information /need – Suresh Atta Sep 11 '15 at 07:11
Thanks allot for the answer. – eatSleepCode Sep 11 '15 at 07:12
So we need to add Discriminator for this table @eatSleepCode ? – Saige Zhang Mar 29 '19 at 04:04

clazz_ attribute in hibernate query

1 Answers1