Question

您好，我是JPA新手并且出现以下错误

In attribute 'employees', the "mapped by" value 'project_id' cannot be resolved to an attribute on the target entity.

以下代码

@Entity
@Table(name = "project")
public class Project {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name = "project_id")
    protected int id;

    @Column(name = "project_name")
    protected String name;

    @ManyToMany(mappedBy = "project_id")
    protected List<Employee> employees;




@Entity
@Table(name = "employee")
public class Employee {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name = "employee_id")
    protected int id;

    @Column(name = "employee_name")
    protected String name;

    @ManyToMany(targetEntity = Project.class)
    @JoinTable(name = "project_employee", joinColumns = @JoinColumn(name = "project_id"), inverseJoinColumns = @JoinColumn(name = "employee_id"))
    protected List<Project> projects;

此处如果我试图映射逆实体，则表示该属性未找到。

请帮我解决这个问题

Answer 1

正如消息所示，您的 mappedBy 值错误。它应该是BIDIRECTIONAL关系另一侧的FIELD / PROPERTY的名称，它链接回此类。例如Project.employees声称通过字段Employee.project_id链接回来，但这并不存在。相反， mappedBy 应为projects。这可以在任何基本的JPA文档中找到

在属性“employees”中，“mapped by”值“project_id”无法解析为目标实体上的属性

1 个答案: