我有一個 RESTful 端點，根據記錄是否已經存在，將使用 JPA 的.save()方法插入新記錄或更新數據庫中的現有記錄。我遇到的問題是，當嘗試更新現有記錄時，JPA 將嘗試訪問不存在的表，employee_department. 我想這是因為在我的Employee實體上我與實體有@ManyToOne關系Department。僅當我嘗試將所有Employee model數據（從 POST 請求發送的數據）映射到Employee entity. 我會得到一個錯誤，即數據庫中沒有名為employee_department. 相反，如果我創建一個擴展 JPAfindByEmail(employee.getEmail())的方法EmployeeRepository，并嘗試將該數據直接保存回數據庫，則不會出現錯誤。model -> entity我的問題是，與僅從數據庫返回記錄并保存相比，在嘗試保存之前映射可能會丟失什么？這是來自client -> controller -> service -> mapper然后返回到客戶端的數據流。POST 請求中的客戶端 JSON{  "id": 109,"isActive": true,"manager": null,"firstName": "string","middleInitial": null,"lastName": "string","department": {  "id": 101},"jobTitle": {  "id": 1001},"email": "g","skypeName": "g","isManager": false}客戶端 -> 員工控制器@RestController@RequestMapping("/emps")public class EmployeeController {    @Autowired    EmployeeService employeeService;    @RequestMapping(method = {RequestMethod.POST, RequestMethod.PUT})    public Employee createOrUpdateEmployee(@RequestBody Employee employee) {        return employeeService.storeOrUpdate(employee);    }員工控制器 -> 員工服務@Servicepublic class EmployeeService {    @Autowired    private EmployeeRepository employeeRepository;    @Autowired    EmployeeMapper employeeMapper;    public Employee storeOrUpdate(Employee employee) {        EmployeeEntity employeeEntity = employeeMapper.modelToEntity(employee);        EmployeeEntity savedEmployeeEntity = employeeRepository.save(employeeEntity);        Employee employeeModel = employeeMapper.entityToModel(savedEmployeeEntity);        return employeeModel;    }Employee正在“更新”的內容直接來自數據庫，那么一切都像魅力一樣。