为什么我的查询响应返回空值？

Question

public class Customer implements Serializable {

    /**
     * 
     */
    private static final long serialVersionUID = 8348682056500740593L;
    @Id
    @GeneratedValue(strategy=GenerationType.IDENTITY)
    private Long id;
    
    private String firstName ;
    private String lastName;

public interface CustomerInter {
    
    String getFirstName();
    String getLastName();
    
}

@Repository
public interface CustomerAccountRepo extends JpaRepository <Customer, Long  > 

{

     Optional<Customer> findById(Long id);
     
    // Optional<Customer> findByFirstNameAndLastName(String firstName , String lastName);

     
     @Query(value="select c.firstName, c.lastName from Customer c")
     List<CustomerInter> findByFirstNameAndLastName();
}

@Service
public class CustomerAccountService {
    
    @Autowired  
    private CustomerAccountRepo custRepo;



    public List<CustomerInter> getFirstNameAndLastNameOnly() throws Exception {
    //    LOGGER.info("Inside getAllCustomerFirst&LastName");
        List<CustomerInter> customerName = custRepo.findByFirstNameAndLastName();
        return customerName;
        }
    
  }

@CrossOrigin(origins = {"http://localhost:3000"})
@RestController
public class CustomerController {
    
        @Autowired
        CustomerAccountService customerRepo;
    
        @GetMapping(value="/customerFirstAndLastName")
         public List<CustomerInter> getFirstNameAndLastNameOnly() throws Exception
         {
             
            return customerRepo.getFirstNameAndLastNameOnly();
             
         }

Answer 1

你想做的事情不会这样做的。

首先，您有一个JParepository ，实体的类型是customer和idlong。因此，JPAREPO的查询将只处理Customer对象。

如果只需要具有firstname和lastname的对象，那么创建一个class(DTO)，只包含这些对象，并将查询更改为：

....

@Query(value="SELECT new path.to.your.package.CustomerDTO(c.firstName, c.lastName) " +
        "FROM Customer c")
     List<CustomerDTO> findByFirstNameAndLastName();