java - hibernate 查询中的 clazz_ 属性

Question

在 Hibernate 表中，每个具体类策略在使用父类(super class)提取时生成以下查询:

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_ 是在表中和类中都没有的查询中选择的，这个 clazz_ 属性是什么？

Answer 1

这就是继承鉴别器。

当您将子类与父类(super class)结合在一起时，请避免在从结果集实例化时发生混淆，hibernate 在内部使用列 'clazz'。