首先：我正在使用Spring-Boot Data JPAJava 8。我的數(shù)據(jù)庫(kù)中有一個(gè)表，我的實(shí)體定義如下：@Entity@Table(name="ITEMHOURS")public class ItemHoursEntity {    @Id    @GeneratedValue(strategy = GenerationType.IDENTITY)    @Column(name = "ID")    private int id;    @Column(name = "YEAR", nullable = false)    private String year;    @Enumerated(EnumType.STRING)    @Column(name = "STATE", nullable = false)    private TypeEnum type;    @Column(name = "HOURVALUE", nullable = false)    private int hourValue = 0;    @ManyToOne(cascade = CascadeType.MERGE)    @JoinColumn(name = "ITEM_ID")    private MyItem item;//.. some more columns, getters, setters...}現(xiàn)在我得到以下選擇返回這個(gè)結(jié)構(gòu)：-----------------------| YEAR | Value | Type |-----------------------@Query(value = "Select year as year, sum(hourvalue) as value, state as type from ITEMHOURS h where item_id = :item_id group by h.year, h.state", nativeQuery = true)    public Optional<Collection<TotalValuesProjection>> getYearTotalsForStateByItem(@Param("item_id") int item_id);它在我的MySQL Workbench. 對(duì)于結(jié)果，我聽說我應(yīng)該ItemHoursEntity通過使用投影來實(shí)現(xiàn)獲取與默認(rèn)不同的結(jié)果，所以我嘗試創(chuàng)建以下內(nèi)容：@Projection(types = { ItemHoursEntity.class })public interface TotalValuesProjection {    public String getYear();    public int getValue();    public HourTypeEnum getType();}現(xiàn)在在我的service班級(jí)中，我嘗試以下方法：@Overridepublic List<ExtendedDataPasser<String, Integer, String>> getTotalAndYearHourValuesForItem(int itemId) {    Optional<Collection<TotalValuesProjection>> projectionOptional = this.hoursRepository.getYearTotalsForStateByItem(itemId);    List<ExtendedDataPasser<String, Integer, String>> entityList = new ArrayList<ExtendedDataPasser<String, Integer, String>>();    projectionOptional.orElseGet(() -> new ArrayList<TotalValuesProjection>()).forEach(entity -> {        entityList.add(new ExtendedDataPasser<String, Integer, String>(entity.getYear(), entity.getValue(), entity.getType().toString()));    });    return entityList;}