我在javaspring中有一个问题，当使用一对一关系时，为什么我不能将khachHang类中的用户名Map到登录类，尽管login. getName不为null，我已经尝试了很多次，但它是错误的，CCCD可以导入到Login类，但khachHang无法获得Login的变量。这个错误是什么意思。谢谢。
这是我的Login类：

@Entity
@Data
@NoArgsConstructor
@AllArgsConstructor
@Table(name = "Login")
public class Login {

    @Id
    private String username;

    private String password;
    private boolean role;

    @OneToOne
    @JoinColumn(name = "CCCD", referencedColumnName = "CCCD")
    private KhachHang khachHang;

    public Login(String username, String password, boolean role) {
        this.username = username;
        this.password = password;
        this.role = role;
    }
}

字符串
这是我的KhachHang类：

@Entity
@Data
@NoArgsConstructor
@AllArgsConstructor
@Table(name = "ThongTinKhachHang")
public class KhachHang {

    @Id
    private String CCCD;

    private String tenKhachHang;
    private boolean gioiTinh;
    private String diaChi;
    private String email;
    private String soDienThoai;

    @OneToOne(mappedBy = "khachHang")
    @JoinColumn(name = "username", referencedColumnName = "username")
    private Login login;

    @OneToMany(mappedBy = "khachHang", cascade = CascadeType.ALL)
    private List<ChiTietDatTour> chiTietDatTours;

    public KhachHang(String CCCD, String tenKhachHang, boolean gioiTinh, String diaChi, String email, String soDienThoai, Login login) {
        this.CCCD = CCCD;
        this.tenKhachHang = tenKhachHang;
        this.gioiTinh = gioiTinh;
        this.diaChi = diaChi;
        this.email = email;
        this.soDienThoai = soDienThoai;
        this.login = login;
    }
}

型
这是从数据库.

查询的结果
更新：我已经更新了保存到数据库逻辑：

@PostMapping("/signup/userSignUp")
    public String userSaveToDatabase(@RequestParam(name = "hoTen") String hoTen,
                                     @RequestParam(name = "username") String username,
                                     @RequestParam(name = "phonenumber") String phoneNumber,
                                     @RequestParam(name = "CCCD") String CCCD,
                                     @RequestParam(name = "email") String email,
                                     @RequestParam(name = "diachi") String diaChi,
                                     @RequestParam(name = "password") String password,
                                     @RequestParam(name = "reconfirm") String reconfirm,
                                     @RequestParam(name = "gioiTinh") boolean gioiTinh,
                                     Model model) {

        if (loginDAO.existsByUsername(username)) {
            model.addAttribute("error", "Username already exists.");
            return "redirect:/signup";
        }

        if (!password.equals(reconfirm)) {
            model.addAttribute("error", "Password and reconfirm password do not match.");
            return "redirect:/index";
        }

        if (!loginDAO.existsCCCD(CCCD).isEmpty()) {
            model.addAttribute("error", "CCCD already exists.");
            return "redirect:/book";
        }

        if (!checkPassword(password) || !validateEmail(email) ||
                !checkCCCD(CCCD) || !checkPhone(phoneNumber) || !checkAddress(diaChi)) {
            return "redirect:/test3";
        }

        Login login = new Login(username, password, false);
        KhachHang khachHang = new KhachHang(CCCD, hoTen, gioiTinh, diaChi, email, phoneNumber, login);

        login.setKhachHang(khachHang);
        khachHang.setLogin(login);

        khachHangDAO.save(khachHang);
        loginDAO.save(login);

        return "redirect:/test2";
    }

型