我有一个关于JPA继承的问题,是否有可能使用join策略来实现这个层次结构?
下面是我的代码:
@Entity
@Table(name = "PERSON")
@Inheritance(strategy = InheritanceType.JOINED)
@DiscriminatorColumn(name = "DTYPE", discriminatorType = DiscriminatorType.STRING, length = 4)
public abstract class Person implements Serializable {
...
}
@Entity
@Table(name = "EMPLOYEE")
@DiscriminatorValue(value="EMPL")
public abstract class Employee extends Person implements Serializable{
...
}
@Entity
@Table(name="CLIENT")
@DiscriminatorValue(value="CLIE")
public class Client extends Person implements Serializable{
...
}
@Entity
@Table(name="TEACHER")
@DiscriminatorValue(value="TEAC")
public class Teacher extends Employee implements Serializable{
...
}
在上面的层次结构之后,我尝试使用JPQL进行查询,这是查询:
@Entity
@Table(name="FICHA_EVALUACION")
public class SheetEvaluation implements Serializable{
@OneToOne
private Teacher teacher;
}
此代码从主
运行Query query = entityManager.createQuery("SELECT f FROM SheetEvaluation f, Teacher teac, Employee emp, Person per WHERE f.teacher.id = teac.id and teac.id = emp.id and emp.id = per.id");
List<SheetEvaluation> sheetEvaluations = query.getResultList();
for (SheetEvaluation sheetEvaluation : sheetEvaluations ) {
System.out.println(" Teacher Name= " + sheetEvaluation .getTeacher().getName());
}
当我运行查询时抛出以下错误
由以下原因引起:com.mysql.jdbc.exceptions.jdbc4. jdbc4. jdbc4. jdbc4。MySQLSyntaxErrorException:未知列employee1_。DTYPE' in 'field list'
如果你有任何关于错误类型的想法,我非常感谢你的支持。
我不是hibernate专家,但是我认为当你使用每类表时,你不能使用@DiscriminatorColumn
,只有当你对所有继承的类都有一个类并且想要区分它们时才需要。
查看单表连接。
在当前join中,它将为所有类创建一个表,并且将有person fk。
@Entity
@Table(name = "PERSON")
@Inheritance(strategy = InheritanceType.JOINED)
public class Person implements Serializable {
...
}
@Entity
@Table(name = "EMPLOYEE")
public class Employee extends Person implements Serializable{
...
}
@Entity
@Table(name="CLIENT")
public class Client extends Person implements Serializable{
...
}
@Entity
@Table(name="TEACHER")
public class Teacher extends Employee implements Serializable{
...
}