Question

我有一个带有两个子类的抽象父类，我希望子类拥有自己的表。我还有另一个与父类有关系的类：

// Class that has the mapping to the abstract class
@Entity
@Table(name="telephone_numbers")
public class TelephoneNumber implements Serializable {

    @Id
    @Column(name="number")
    private String number;

    @Column(name="originating_carrier")
    private String originatingCarrier;

    @OneToOne(mappedBy = "number")
    private TelephoneNumberAssignment assignment;

... getters and setters ...

}

// Classes involved in inheritance
public abstract class TelephoneNumberAssignment implements Serializable {

    @Id
    @OneToOne
    @JoinColumn(name="number")
    private TelephoneNumber number;

        ... getters and setters ...
}

@Entity
@Table(name="telephone_numbers_fixed_line")
@Inheritance(strategy=InheritanceType.TABLE_PER_CLASS)
public class FixedLineNumberAssignment extends TelephoneNumberAssignment {

    @Column(name="recorded")
    private Boolean recorded;

    public FixedLineNumberAssignment() {
    }

        ... getters and setters ...

}

@Entity
@Table(name="telephone_numbers_mobile")
@Inheritance(strategy=InheritanceType.TABLE_PER_CLASS)
public class MobileNumberAssignment extends TelephoneNumberAssignment {

    @ManyToOne
    @JoinColumn(name = "customer_id")
    private Customer customer;

    public MobileNumberAssignment() {
    }

        ... getters and setters ...

}

根据this question的答案，为了让我的超类中的JPA注释转移到子类，我需要使用@MappedSuperclass。但是，由于需要映射到超类，会发生以下异常：

Caused by: org.hibernate.AnnotationException: Unknown mappedBy in: com.vtsl.domain.numbering.TelephoneNumber.assignment, referenced property unknown: com.vtsl.domain.numbering.TelephoneNumberAssignment.number

根据this question的答案，我可以使用TABLE_PER_CLASS来解决此问题。但是，如果我这样做，我的超类JPA注释似乎不会延续;如果我执行JPQL查询

return entityManager.createQuery("SELECT mob FROM MobileNumberAssignment as mob INNER JOIN FETCH mob.number", MobileNumberAssignment.class).getResultList();

返回的结果没有填充number字段（进一步检查时，我发现hibernate在尝试解析结果对象的属性时没有检测到number属性）。但是，当我执行以下操作时：

//Result set has 1 object
entityManager
    .createQuery("SELECT mob FROM MobileNumberAssignment as mob INNER JOIN FETCH mob.number WHERE mob.number.number = :number", MobileNumberAssignment.class)
    .setParameter("number", "number that exists")
    .getResultList()

//Result set has 0 object
entityManager
    .createQuery("SELECT mob FROM MobileNumberAssignment as mob INNER JOIN FETCH mob.number WHERE mob.number.number = :number", MobileNumberAssignment.class)
    .setParameter("number", "number that does not exist")
    .getResultList()

结果似乎表明该参数毕竟成功解决了。

为什么number属性不会被填充？

Answer 1

看来我从症状中得出了所有错误的结论。问题根本不在于继承规范，而在于映射主键的规范。根据我发现的每一种资源

@Id
@OneToOne
@JoinColumn(name="number")
private TelephoneNumber number;

应该工作得很好，但似乎在我使用的hibernate版本（4.10）它没有。更改映射以使用@MapsId解决了我正在观察的问题，使新的（现在正在工作的）TelephoneNumberAssignment看起来像：

@Entity
@Inheritance(strategy=InheritanceType.TABLE_PER_CLASS)
public abstract class TelephoneNumberAssignment implements Serializable {

    @Id String numberString;

    @MapsId
    @OneToOne
    @JoinColumn(name="number")
    private TelephoneNumber number;

    ... getters and setters ...
}

JPA继承：Mapped Superclass vs Table Per Class

1 个答案: