我有几个实体：

@Entity
@Table(name = "app_user", schema = "edu", catalog = "ed_db")
@Getter
@Setter
public class AppUser {
   @Basic
    @GeneratedValue(strategy = GenerationType.SEQUENCE)
    @Column(name = "id", insertable = false, updatable = false)
    private Integer id;
    @Id
    @Column(name = "username")
    private String username;
    @Basic
    @Column(name = "password")
    @JsonIgnore
    private String password;
    @Basic
    @Column(name = "first_name")
    private String firstName;
    @Basic
    @Column(name = "last_name")
    private String lastName;
    @Basic
    @Column(name = "email")
    private String email = "";

}

和教师实体，教师实体与appuser的关系为：

@Entity
@Getter
@Setter
public class Teacher {
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Id
    @Column(name = "id")
    private Integer id;

    @ManyToOne(fetch = FetchType.LAZY, optional = false)
    @OnDelete(action = OnDeleteAction.CASCADE)
    @JoinColumn(name = "app_user_id", nullable = false, referencedColumnName = "id")
    private AppUser appUser;

    @Basic
    @Column(name = "client_id")
    @NotNull(message = "client.is_required")
    private Integer clientId;

}

当我尝试在代码中使用它时：

public Teacher save(TeacherDto teacherDto) {
        AppUser appUser = teacherDto.getAppUserEntity();
        AppUser dbAppUser = appUserService.save(appUser);
        Teacher teacher = teacherDto.getTeacherEntity();
        teacher.setAppUser(dbAppUser);
        teacher.setClientId(appUser.getClientId());

        return teacherRepository.save(teacher);
    }

它不断抛出异常：

2022-08-19T01:20:56.052-04:00  WARN 69525 --- [nio-8080-exec-2] o.h.engine.jdbc.spi.SqlExceptionHelper   : SQL Error: 0, SQLState: 23502
2022-08-19T01:20:56.053-04:00 ERROR 69525 --- [nio-8080-exec-2] o.h.engine.jdbc.spi.SqlExceptionHelper   : ERROR: null value in column "app_user_id" of relation "teacher" violates not-null constraint
  Detail: Failing row contains (1, null, 2, 2022-08-19 01:20:56.028, 2022-08-19 01:20:56.028).
2022-08-19T01:20:56.064-04:00 ERROR 69525 --- [nio-8080-exec-2] c.c.p.exceptions.GlobalExceptionHandler  : org.springframework.dao.DataIntegrityViolationException: could not execute statement; SQL [n/a]; constraint [app_user_id" of relation "teacher]

我不知道这里有什么问题。在控制台中，语句如下所示：

insert 
    into
        edu.app_user
        (address, client_id, created_at, email, enabled, first_name, last_name, password, phone, username) 
    values
        (?, ?, ?, ?, ?, ?, ?, ?, ?, ?)
insert 
    into
        edu.teacher
        (app_user_id, client_id, created_at, updated_at) 
    values
        (?, ?, ?, ?)