spring-data-jpa dto 中的 classcastexception

Question

我无法将 JPA ResultSet 转换为 DTO。当我从数据库中获取值，但使用 toString() 方法打印值时，我得到了 ClassCastException：

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;
    }
}

在调试时，我发现cityListing 正在被填充。

有什么建议吗？

Answer 1

此查询将返回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);

我相信根据您的堆栈跟踪，responseCityList.add(s); 正在尝试将 s 转换为 CityEntity 并且失败了。

请将您的查询更新为此。

@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);