Spring数据JPA保存更新父实体

Question

学生.java

@Entity

@Table(name = "Student")

@Data

@NoArgsConstructor

public class Student implements Serializable {

   @Id

   @GeneratedValue(strategy = GenerationType.IDENTITY)

   private Long id;

   @OneToMany(mappedBy = "studentId", cascade = CascadeType.ALL)

   private List<Subject> subjectList = new ArrayList<>();

   public void addSubject(Subject subject) {

     subjectList.add(subject);

     subject.setStudentId(this);

   }

   @Column(name = "firstName")

   private String firstName;

   @Column(name = "lastName")

   private String lastName;

}

Subject.java

@Entity

@Table(name = "Subject")

@Data

@NoArgsConstructor

public class Subject implements Serializable {

   @Id

   @GeneratedValue(strategy = GenerationType.IDENTITY)

   private Long id;

   @ManyToOne(fetch = FetchType.LAZY)

   @JoinColumn(name="studentId", nullable = false)

   private Student studentId;

   @Column(name = "subjectName")

   private String subjectName;

   @Column(name = "subjectCode")

   private int subjectCode;

}

SubjectRepository.java

@Repository

public interface SubjectRepository extends JpaRepository<Subject, Long> {

}

如上面的代码结构所示，我有2个实体（Student，Subject）和一个存储库类（SubjectRepository）。当我尝试保存到“主题”表中时，数据库中的“学生”表中的学生姓名“ Thomas”也会以某种方式得到更新。我只想插入Subject表，而没有更新Student表中的任何值。需要一些帮助。谢谢！

public static void main(String[] args) {

    @Autowired protected SubjectRepository subjectRepository;

    Student student = new Student();

    student.setFirstName("Thomas");

    Subject subject = new Subject();

    subject.setSubjectName("Chemistry");

    subject.setSubjectCode(12345);

    student.addSubject(subject)

    subjectRepository.save(subject)

}