spring-data-jpa上的classcast異常dto

Question

我無法將JPA ResultSet轉換爲DTO。雖然我正在從數據庫值，但使用toString（）方法印製的價值觀，我得到ClassCastException異常：

java.lang.ClassCastException: [Ljava.lang.Object; cannot be cast to com.practice.entity.CityEntity 
    at java.util.ArrayList.forEach(Unknown Source) ~[na:1.8.0_91] 
    at com.practice.service.CityService.getCities(CityService.java:47) ~[classes/:na] 

---

@Service 
public class CityService { 
..... 

      cityListing = cityDAO.citylisting(countryName); 

      cityResponse.setCityCount(cityListing.size()); 


    cityListing.forEach(s -> { 
       System.out.println(s); 
       responseCityList.add(s); 
      }); 

---

@Repository("cityDAO") 
public interface CityManipulationDAO extends JpaRepository<CityEntity, Integer>{ 

    @Query("Select a.id, a.name, a.district,a.countrycode, a.population from CityEntity a where a.countrycode.CountryName=:countryName") 
    //List of cities for particular countries 
    public List<CityEntity> citylisting(@Param("countryName") String Name); 

} 

@Entity 
@Table(name="city") 
public class CityEntity { 

    @Id 
    private Integer id; 

    @Column 
    private String name; 

    @ManyToOne(optional=true, fetch=FetchType.LAZY) 
    @JoinColumn(name="countrycode", referencedColumnName="code") 
    private CountryEntity countrycode; 

    @Column 
    private String district; 

    @Column 
    private Integer population; 
... 

    @Override 
    public String toString() { 
     return id+","+name+","+district+","+population; 
    } 
} 

在調試，我發現cityListing越來越填充。

有什麼建議嗎？

Answer 1

此查詢將返回List<Object[]>。

@Query("Select a.id, a.name, a.district,a.countrycode, a.population from CityEntity a where a.countrycode.CountryName=:countryName") 
//List of cities for particular countries 
public List<CityEntity> citylisting(@Param("countryName") String Name); 

我相信基於關閉您的堆棧跟蹤的是responseCityList.add(s);試圖投s到CityEntity和失敗。

請更新您的查詢。

@Query("Select a from CityEntity a where a.countrycode.CountryName=:countryName") 
//List of cities for particular countries 
public List<CityEntity> citylisting(@Param("countryName") String Name);