我有一个country和state表，我已经与spring数据jpa进行了集成。我已经创建了一个函数 public Page<CountryDetails> getAllCountryDetails 在我的countryserviceinmpl中获取所有国家和相应的州详细信息。服务运行良好，并提供以下输出：

{
  "content": [
    {
      "id": 123,
      "countryName": "USA",
      "countryCode": "USA",
      "countryDetails": "XXXXXXXX",
      "countryZone": "XXXXXXX",
      "states": [
        {
          "id": 23,
          "stateName": "Washington DC",
          "countryCode": "USA",
          "stateCode": "WAS",
          "stateDetails": "XXXXX",
          "stateZone": "YYYYYY"
        },
        {
          "id": 24,
          "stateName": "Some Other States",
          "countryCode": "USA",
          "stateCode": "SOS",
          "stateDetails": "XXXXX",
          "stateZone": "YYYYYY"
        }
      ]
    }
  ],
  "last": false,
  "totalPages": 28,
  "totalElements": 326,
  "size": 12,
  "number": 0,
  "sort": null,
  "numberOfElements": 12,
  "first": true
}

我的完整代码如下：
countryrepository.java文件

@Repository
public interface CountryRepository extends JpaRepository<CountryDetails, Integer> {

    @Query(value = "SELECT country FROM Country country GROUP BY country.countryId ORDER BY ?#{#pageable}", 
    countQuery = "SELECT COUNT(*) FROM Country country GROUP BY country.countryId ORDER BY ?#{#pageable}")
    public Page<CountryDetails> findAll(Pageable pageRequest);
}

countryserviceimpl.java版本

@Service
public class CountryServiceImpl implements CountryService {

    @Autowired
    private CountryRepository countryRepository;

    @Override
    public Page<CountryDetails> getAllCountryDetails(final int page, final int size) {
        return countryRepository.findAll(new PageRequest(page, size));
    }
}

countrydetails.java文件

@Entity
@Table(name = "country", uniqueConstraints = @UniqueConstraint(columnNames = "id"))
public class CountryDetails {

    @Id
    @GeneratedValue
    @Column(name = "id", unique = true, nullable = false)
    private Integer id;
    private String countryName;
    private String countryCode;
    private String countryDetails;
    private String countryZone;

    @JsonManagedReference
    @OneToMany(fetch = FetchType.LAZY, mappedBy = "countryDetails")
    private List<State> states;

    // getters / setters omitted
}

状态.java

@Entity
@Table(name = "state", uniqueConstraints = @UniqueConstraint(columnNames = "id"))
public class State {

    @Id
    @GeneratedValue
    @Column(name = "id", unique = true, nullable = false)
    private Integer id;
    private String stateName;
    private String countryCode;
    private String stateCode;
    private String stateDetails;
    private String stateZone;

    @JsonBackReference
    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "countryCode", nullable = false, insertable = false, updatable = false, foreignKey = @javax.persistence.ForeignKey(name="none",value = ConstraintMode.NO_CONSTRAINT))
    private CountryDetails countryDetails;

    // getters / setters omitted
}

现在问题来了

实际上，我希望国家服务返回如下所示的最低限度的信息

{
  "content": [
    {
      "countryName": "USA",
      "countryCode": "USA",
      "states": [
        {
          "stateCode": "WAS"
        },
        {
          "stateCode": "SOS"
        }
      ]
    }
  ],
  "last": false,
  "totalPages": 28,
  "totalElements": 326,
  "size": 12,
  "number": 0,
  "sort": null,
  "numberOfElements": 12,
  "first": true
}

为了实现这一点，我使用了如下所示的投影
countryprojection.java语言

public interface CountryProjection {
    public String getCountryName();
    public String getCountryCode();
    public List<StateProjection> getStates();
}

stateprojection.java语言

public interface StateProjection {
    public String getStateCode();
}

countryserviceimpl.java版本

@Repository
public interface CountryRepository extends JpaRepository<CountryDetails, Integer> {

    @Query(value = "SELECT country.countryName AS countryName, country.countryCode AS countryCode FROM Country country GROUP BY country.countryId ORDER BY ?#{#pageable}", 
    countQuery = "SELECT COUNT(*) FROM Country country GROUP BY country.countryId ORDER BY ?#{#pageable}")
    public Page<CountryProjection> findAll(Pageable pageRequest);
}

但是现在服务返回如下所示的任何状态详细信息

{
  "content": [
    {
      "countryName": "USA",
      "countryCode": "USA"
    }
  ],
  "last": false,
  "totalPages": 28,
  "totalElements": 326,
  "size": 12,
  "number": 0,
  "sort": null,
  "numberOfElements": 12,
  "first": true
}

我们怎样才能得到如下所示的最小状态细节

{
  "content": [
    {
      "countryName": "USA",
      "countryCode": "USA",
      "states": [
        {
          "stateCode": "WAS"
        },
        {
          "stateCode": "SOS"
        }
      ]
    }
  ],
  "last": false,
  "totalPages": 28,
  "totalElements": 326,
  "size": 12,
  "number": 0,
  "sort": null,
  "numberOfElements": 12,
  "first": true
}

有人能帮我吗