我有一個(gè) RESTful 端點(diǎn)，根據(jù)記錄是否已經(jīng)存在，將使用 JPA 的.save()方法插入新記錄或更新數(shù)據(jù)庫(kù)中的現(xiàn)有記錄。我遇到的問(wèn)題是，當(dāng)嘗試更新現(xiàn)有記錄時(shí)，JPA 將嘗試訪問(wèn)不存在的表，employee_department. 我想這是因?yàn)樵谖业腅mployee實(shí)體上我與實(shí)體有@ManyToOne關(guān)系Department。僅當(dāng)我嘗試將所有Employee model數(shù)據(jù)（從 POST 請(qǐng)求發(fā)送的數(shù)據(jù)）映射到Employee entity. 我會(huì)得到一個(gè)錯(cuò)誤，即數(shù)據(jù)庫(kù)中沒(méi)有名為employee_department. 相反，如果我創(chuàng)建一個(gè)擴(kuò)展 JPAfindByEmail(employee.getEmail())的方法EmployeeRepository，并嘗試將該數(shù)據(jù)直接保存回?cái)?shù)據(jù)庫(kù)，則不會(huì)出現(xiàn)錯(cuò)誤。model -> entity我的問(wèn)題是，與僅從數(shù)據(jù)庫(kù)返回記錄并保存相比，在嘗試保存之前映射可能會(huì)丟失什么？這是來(lái)自client -> controller -> service -> mapper然后返回到客戶端的數(shù)據(jù)流。POST 請(qǐng)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(wù)@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(nèi)容直接來(lái)自數(shù)據(jù)庫(kù)，那么一切都像魅力一樣。