1
我试图用继承策略TABLE_PER_CLASS映射JPA(使用Hibernate)一对一关系。下面是一个例子:当我打电话“findMansDrivingLicenses”检索所有男人的驾驶执照冬眠做一个“UNION ALL”有两个表(MAN和突变)在一对一关系上查询JPA TABLE_PER_CLASS映射
@Entity
public class DrivingLicense {
@OneToOne(targetEntity = Human.class, cascade = CascadeType.ALL, fetch=FetchType.LAZY)
@JoinColumn
private Human human;
@SuppressWarnings("unchecked")
public static List<DrivingLicense> findMansDrivingLicenses(Long id) {
if (id == null) return null;
return entityManager()
.createQuery("select o from DrivingLicense o left join fetch o.human where o.id = :id")
.setParameter("id", id)
.getResultList();
}
}
@Entity
@Inheritance(strategy = InheritanceType.TABLE_PER_CLASS)
public abstract class Human {
...
}
@Entity
public class Man extends Human {
...
}
@Entity
public class Mutant extends Human {
...
}
。按照日志输出:
select
drivinglic0_.id as id3_0_,
human1_.id as id0_1_,
drivinglic0_.first_name as first2_3_0_,
drivinglic0_.human as human3_0_,
drivinglic0_.last_name as last3_3_0_,
drivinglic0_.type as type3_0_,
drivinglic0_.version as version3_0_,
human1_.version as version0_1_,
human1_.comment as comment1_1_,
human1_.behavior as behavior2_1_,
human1_.clazz_ as clazz_1_
from
driving_license drivinglic0_
left outer join
(
select
id,
version,
comment,
null as behavior,
1 as clazz_
from
man
union
all select
id,
version,
null as comment,
behavior,
2 as clazz_
from
mutant
) human1_
on drivinglic0_.human=human1_.id
where
drivinglic0_.id=?
有什么办法来防止休眠做到这一点“UNION ALL”,只有与MAN表加入?
查询修改,仍然加入(联合所有)与表男人和突变::( 增加@ org.hibernate.annotations.Entity(多态性= PolymorphismType.EXPLICIT),没有任何东西! – monit06 2010-06-30 19:36:45
@ monit06我很确定它发生是因为你有一个** TABLE_PER_CLASS **策略。因为**身份必须保证**,所以Hibernate确保所有的子类不会返回相同的身份。如果你真的想避免这种行为,你应该使用MappedSuperclass而不是继承。 – 2010-06-30 20:43:09
@ monit06或使用** SINGLE_TABLE **策略。加入战略也有同样的问题。 – 2010-06-30 20:48:24