Question

我尝试使用多个映射属性。但是当我尝试运行代码时，代码会生成异常，这个例子是基于Pro JPA 2，第10章的书。有以下代码：

DeptID.java

public class DeptId implements Serializable{

private static final long serialVersionUID = 5177373337405448966L;
private int number;
private String country;
    .....................

ProjectId.java

public class ProjectId implements Serializable{

private static final long serialVersionUID = 4239980609226293562L;
private String name;
private DeptId deptId;
.....................

Department.java

@Entity
@IdClass(DeptId.class)
public class Department implements Serializable {

private static final long serialVersionUID = 1L;
@Id
private int number;
@Id
private String country;
private String name;

@OneToMany(mappedBy="deptId")
List<Project> projects;
    ......................

Project.java

@Entity
@IdClass(ProjectId.class)
public class Project implements Serializable {

private static final long serialVersionUID = 1L;
@Id
private String name;

@Id
@ManyToOne
@JoinColumn(name="dept_id")
private Department deptId;
    ........................

此代码将生成以下异常

Caused by: org.hibernate.AnnotationException: Implicit column reference in the @MapsId mapping fails, try to use explicit referenceColumnNames: example.domain.Department

Answer 1

DeptID有两个主键，因此您不能拥有@JoinColumn(name="dept_id")之类的内容。相反，使用这个：

@JoinColumns({
    @JoinColumn(name="dept_number", referencedColumnName="number"),
    @JoinColumn(name="dept_country", referencedColumnName="country")
})

如果仍然不起作用：在主键类（DeptID＆amp; ProjectId）中尝试切换到public或保护私有属性。还检查他们是否有一个没有参数的构造函数，并实现equals＆amp;哈希码方法。

JPA 2：@MapsId映射中的隐式列引用失败

1 个答案: