具有第三实体关系的弹簧后误差

Question

我是春天的新人，我想用这个结构来存储考试和试题之间的关系：

@Entity
@Data
@EqualsAndHashCode(callSuper = true)
public class Exam extends UriEntity<Integer> {

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

  @NotBlank
  @Length(min = 1, max = 256)
  private String name;

  @OneToMany(mappedBy="exam")
  private List<ExamQuestion> exams_questions;

@Entity
@Data
@EqualsAndHashCode(callSuper = true)
public class Question extends UriEntity<Integer> {

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

  @NotBlank
  @Column(unique = true)
  private String statement;

  @NotBlank
  private String answer;

  @OneToMany(mappedBy="question")
  private List<ExamQuestion> exams_questions;

@Entity
@Data
@EqualsAndHashCode(callSuper = true)
public class ExamQuestion extends UriEntity<Integer> {

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

  @ManyToOne
  @JoinColumn(name = "question_id")
  private Question question;

  @ManyToOne
  @JoinColumn(name = "exam_id")
  private Exam exam;

当我想用邮递员存储一个新的ExamQuestion对象时

{
  "exam": "http://localhost:8080/exams/28",
  "question": "http://localhost:8080/questions/17"
}

我收到一个错误409，消息是：

NULL不允许列\"ID\"；

有人能帮我吗？提前谢谢。

Answer 1

这可能是因为@GeneratedValue(strategy = GenerationType.IDENTITY)。

确保在数据库架构ID列中设置为自动递增，因为GenerationType.IDENTITY使用数据库标识列生成值。因此，如果您的列未被设置为自动递增，则会得到此错误。