spring data jpa如何只查询实体部分字段

package com.qianyucc.blog.model;
import lombok.*;
import javax.persistence.*;
/**
 * @author lijing
 * @date 2019-08-05 14:28
 * @description 文章
 */
@Data
@Entity
@Table(name = "article")
public class Article {
    @Id
    // 主键自增
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    @Column(name = "author",unique = false,nullable = false,length = 20)
    private String author;
    @Column(name = "title",length = 100)
    private String title;
    @Column(name = "content",columnDefinition = "clob not null")
    private String content;
    @Column(name = "tags",length = 50)
    private String tags;
    @Column(name = "type")
    private Integer type;
    @Column(name = "categories",length = 50)
    private String categories;
    @Column(name = "gmt_create")
    private Long gmtCreate;
    @Column(name = "gmt_update")
    private Long gmtUpdate;
    @Column(name = "tabloid")
    private String tabloid;
    @Column(name = "likes")
    private Integer likes;
    @Column(name = "views")
    private Integer views;
}

package com.qianyucc.blog.controller;
/**
 * @author lijing
 * @date 2019-08-05 15:13
 * @description
 */
@RestController
public class ArticleController {
    @Autowired
    private ArticleRepositoryarticleRepository;
    @GetMapping("/getAllCategories")
 public Object getAllCategories(){
     return articleRepository.getAllCategories();
 }
}

package com.qianyucc.blog.repository;
import com.qianyucc.blog.model.*;
import org.springframework.data.jpa.repository.*;
import java.util.*;
/**
 * @author lijing
 * @date 2019-08-05 14:28
 * @description 文章数据库访问层
 */
public interface ArticleRepository extends JpaRepository<Article,Long>,JpaSpecificationExecutor<Article> {
    @Query(value = "select distinct categories from article",nativeQuery = true)
    // 这里注意返回值用String类型接收
    List<String> findAllCategories();
}

public interface ArticleRepository extends JpaRepository<Article,Long>,JpaSpecificationExecutor<Article> {
    @Query(value = "select author,categories from article",nativeQuery = true)
    List<Map<String,Object>> findAllCategories();
}