如何在Spring Boot中使用CrudRepository获取最新的5篇文章

Question

@Entity
public class Post {
    @Id
    @GeneratedValue(strategy=GenerationType.AUTO)
    private Long id;

    @Column(nullable=false, length=300)
    private String title;

    @Column(nullable=false)
    private String body;

    @ManyToOne(optional=false, fetch=FetchType.LAZY)
    private Users author;

    @Column(nullable=false)
    private Date date= new Date();

    public Post(){

    }

    public Post(Long id,String title, String body, Users author){
        this.id=id;
        this.title=title;
        this.body=body;
        this.author=author;
    }

    public Long getId() {
        return id;
    }

    public void setId(Long id) {
        this.id = id;
    }

    public String getTitle() {
        return title;
    }

    public void setTitle(String title) {
        this.title = title;
    }

    public String getBody() {
        return body;
    }

    public void setBody(String body) {
        this.body = body;
    }

    public Users getAuthor() {
        return author;
    }

    public void setAuthor(Users author) {
        this.author = author;
    }

    public Date getDate() {
        return date;
    }

    public void setDate(Date date) {
        this.date = date;
    }

    @Override
    public String toString() {
        return "Post [id=" + id + ", title=" + title + ", body=" + body + ", author=" + author + ", date=" + date + "]";
    }
}

public interface PostRepository extends CrudRepository<Post, Long>{
    List<Post> findById(Long id);
    List<Post> findByAuthor(String author);
}

public interface PostServices {
    List<Post> findLatest5();
}

@Service
public class PostServicesImp implements PostServices{

    @Autowired
    private PostRepository pRepo;

    @Override
    public List<Post> findLatest5() {
//      return pRepo.findLatest5Posts(new PageRequest(0, 5));
        return posts.stream().sorted((a,b)-> b.getDate().compareTo(a.getDate()))
                .limit(5)
                .collect(Collectors.toList());
    }
}

Answer 1

来自Spring Data JPA文档：

限制查询结果

查询方法的结果可以通过关键字first或top来限制，这两个关键字可以互换使用。可以在top/first后面追加一个可选的数值，以指定要返回的最大结果大小。如果省略了该数字，则假定结果大小为1。

User findTopByOrderByAgeDesc();
List<User> findTop10ByLastname(String lastname, Pageable pageable);

List<Post> findTop5ByOrderByDateDesc();