ManyToMany的应用-Spring不起作用

Question

我正在实现用户和权限之间的多对多关系，我无法断定我哪里错了，它不起作用 (Unable to map collection rs.raf.demo.model.User.permissions)：

@Data
@Entity
public class User {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name = "user_id")
    private Long userId;

    @Column
    private String username;

    @Column
    private String password;

    @ManyToMany
    @JoinTable(
            name = "USERS_PERMISSIONS",
            joinColumns = @JoinColumn(name = "USER_ID", referencedColumnName = "ID"),
            inverseJoinColumns = @JoinColumn(name = "PERMISSION_ID", referencedColumnName = "ID")
    )
    private List<Permission> permissions = new ArrayList<>();
}

================================================ ====================================

@Data
@Entity
public class Permission {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name = "permission_id")
    private Long userId;

    private String type;

    @ManyToMany
    @JoinTable(
            name = "USERS_PERMISSIONS",
            joinColumns = @JoinColumn(name = "PERMISSION_ID", referencedColumnName = "ID"),
            inverseJoinColumns = @JoinColumn(name = "USER_ID", referencedColumnName = "ID")
    )
    @JsonIgnore
    private List<User> users = new ArrayList<>();
}

我通过查看此示例实现了用户和权限，这是有效的（我看不出用户和权限的区别）：

@Data
@Entity
@Table(name = "STUD")
public class Student {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    private String lastName;

    private String firstName;

    @ManyToMany
    @JoinTable(
            name = "STUDENTS_COURSES",
            joinColumns = @JoinColumn(name = "STUDENT_ID", referencedColumnName = "ID"),
            inverseJoinColumns = @JoinColumn(name = "COURSE_ID", referencedColumnName = "ID")
    )
    private List<Course> courses = new ArrayList<>();
}

================================================ ===================================

@Data
@Entity
public class Course {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    private String title;

    @ManyToMany
    @JoinTable(
            name = "STUDENTS_COURSES",
            joinColumns = @JoinColumn(name = "COURSE_ID", referencedColumnName = "ID"),
            inverseJoinColumns = @JoinColumn(name = "STUDENT_ID", referencedColumnName = "ID")
    )
    @JsonIgnore
    private List<Student> students = new ArrayList<>();

    public void addStudent(Student student) {
        students.add(student);
        student.getCourses().add(this);
    }

    public void removeStudent(Student student) {
        students.remove(student);
        student.getCourses().remove(this);
    }
}

Answer 1

JPA 为多对多关系使用（并且可能在您的情况下创建）中间连接表，并且您不能使用与您在实体中指定的名称不同的引用列名称。

所以你需要设置：

• 在用户类中

@ManyToMany
    @JoinTable(
            name = "USERS_PERMISSIONS",
            joinColumns = @JoinColumn(name = "USER_ID", referencedColumnName = "USER_ID"),
            inverseJoinColumns = @JoinColumn(name = "PERMISSION_ID", referencedColumnName = "PERMISSION_ID")
    )

• 获得许可

@ManyToMany
    @JoinTable(
            name = "USERS_PERMISSIONS",
            joinColumns = @JoinColumn(name = "PERMISSION_ID", referencedColumnName = "PERMISSION_ID"),
            inverseJoinColumns = @JoinColumn(name = "USER_ID", referencedColumnName = "USER_ID")
    )

• 其他表也一样。