javax.persistence.EntityNotFoundException 级联保存多对多关系时

Question

在我的业务中， Staff和Department之间的关系是many-to-many ， Staff通过DepartmentStaff与Department相关，并且DepartmentStaff在DepartmentStaffId中定义了一个复合主键（ department_id ， staff_id ）。 因为DepartmentStaff有额外的列，所以我不使用@ManyToMany 。 这是实体：

// BaseDTO.java

@MappedSuperclass
@Getter
public class BaseDTO {

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

    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;
        BaseDTO baseDTO = (BaseDTO) o;
        return id != null && id.equals(baseDTO.getId());
    }

    @Override
    public int hashCode() {
        return getClass().hashCode();
    }

}

// Staff.java

@Getter
@Setter
@ToString
@Entity
@Table(name = "staffs")
public class Staff extends BaseDTO implements Serializable {

  // ...
  
  @OneToMany(mappedBy = "staff", fetch = FetchType.LAZY)
  @ToString.Exclude
  private Set<DepartmentStaff> departmentStaffs;

}

// Department.java

@Getter
@Setter
@ToString
@Entity
@Table(name = "departments")
public class Department extends BaseDTO implements Serializable {

  // ...

  @OneToMany(mappedBy = "department", fetch = FetchType.LAZY)
  @ToString.Exclude
  private Set<DepartmentStaff> departmentStaffs;

}

// DepartmentStaffId.java

@Embeddable
@Getter
@Setter
@ToString
public class DepartmentStaffId implements Serializable {

    @Column(name = "department_id")
    private Long departmentId;

    @Column(name = "staff_id")
    private Long staffId;

    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;
        DepartmentStaffId that = (DepartmentStaffId) o;
        return departmentId != null && Objects.equals(departmentId, that.getDepartmentId()) &&
                staffId != null && Objects.equals(staffId, that.getStaffId());
    }

    @Override
    public int hashCode() {
        return Objects.hash(departmentId, staffId);
    }
}

// DepartmentStaff.java

@Getter
@Setter
@ToString
@Entity
@Table(name = "department_staffs")
public class DepartmentStaff implements Serializable {
  
  // ...

  @EmbeddedId
  private DepartmentStaffId departmentStaffId;

  @ManyToOne(fetch = FetchType.LAZY)
  @MapsId("departmentId")
  @JoinColumn(name = "department_id")
  @ToString.Exclude
  private Department department;

  @ManyToOne(fetch = FetchType.LAZY)
  @MapsId("staffId")
  @JoinColumn(name = "staff_id")
  @ToString.Exclude
  private Staff staff;

  @Override
  public boolean equals(Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;
        DepartmentStaff that = (DepartmentStaff) o;
        return departmentStaffId != null && Objects.equals(departmentStaffId, that.getDepartmentStaffId());
    }

    @Override
    public int hashCode() {
        return getClass().hashCode();
    }

}

当我保存新的员工条目时：

// ...
Staff staff = new Staff();
Set<DepartmentStaff> departmentStaffs = new HashSet<>();

DepartmentStaff departmentStaff = new DepartmentStaff();
DepartmentStaffId departmentStaffId = new DepartmentStaffId();

departmentStaffId.setDepartmentId(1L);
departmentStaff.setDepartmentStaffId(departmentStaffId);

departmentStaffs.add(departmentStaff);

staff.setDepartmentStaffs(departmentStaffs);

staffRepository.save(staff);
// ...

它抛出：

Caused by: javax.persistence.EntityNotFoundException: Unable to find com.example.dto.DepartmentStaff with id DepartmentStaffId(departmentId=1, staffId=null)

在我 append cascade = {CascadeType.ALL}到所有@OneToMany定义之后，它抛出

Caused by: org.hibernate.id.IdentifierGenerationException: attempted to assign id from null one-to-one property [com.example.dto.DepartmentStaff.department]

我是 Java 和 Spring 的新手，我的多对多关系配置似乎有问题。 你能告诉我如何解决这个问题。:-)

另一个问题，我在DepartmentStaffId和DepartmentStaff中的equals() / hashCode()定义对吗？