Question

我无法将JPA ResultSet强制转换为DTO。虽然我从数据库获取值，但使用toString（）方法打印值，但我得到的是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正在填充。

任何建议？

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);

我相信基于您的堆栈跟踪responseCityList.add(s);正试图将s投放到CityEntity并失败。

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);

spring-data-jpa dto上的classcast异常

1 个答案: