具有两个抽象类的JPA继承

Question

我有一个关于JPA中继承的问题，是否可以使用JOINED策略来实现这个层次结构？

这是我的代码:

@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;
}  

此代码从主代码运行

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());

}

当我运行该查询时，会抛出以下错误

导致原因:com . MySQL . JDBC . exceptions . JDBC 4 . MySQL syntaxerrorexception:未知列“employee1_。“字段列表”中的“DTYPE”

如果您对获得的错误类型有任何想法，我非常感谢您的支持。

致敬

Answer 1

我不是hibernate大师，但我认为当您为每个类使用表时，您不可能拥有＜code＞鉴别器列，只有当您为所有固有类拥有一个类并且想要区分它们时，才需要它。

查看此单表联接。

在当前联接中，它将为所有类创建表，并将具有人员 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{
...
}