java - 在 Spring Data (MongoDB) 中实现 findOne

Question

我在执行 MongoOperations 类的 findOne 方法时遇到一些问题，目前此方法返回 null。我在 mongoDB 中的数据结构如下所示:

> db.news.find({_id:1})
{ "_id" : 1, "title" : "first title", "text" : "first text" }
> db.news.find({_id:{$type:1}})
{ "_id" : 1, "title" : "first title", "text" : "first text" }

正如您在上面看到的，_id 字段具有 Double 类型。我的 Java 类看起来像这样:

@Repository
public class NewsService {

    @Autowired
    private MongoOperations mongoOperations;

    public static final String COLLECTION_NAME = "news";

    //this method executes ok
    public List<NewsEntity> getAllNews() {
        return mongoOperations.findAll(NewsEntity.class, COLLECTION_NAME);
    }

    //but this method return null     
    public NewsEntity getNewsDetail(Long id) {
        return mongoOperations.findOne(Query.query(Criteria.where("_id").is(id)), NewsEntity.class);
    }

实体类:

@Document
public class NewsEntity {

 @Id
 private Long id;
 private String title;
 private String text;


 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 getText() {
     return text;
 }

 public void setText(String text) {
     this.text = text;
 } 
}

和 Spring Controller :

@Controller
public class MainController {
 @Autowired
 private NewsService newsService;

 @RequestMapping(value="/news/details/{newsId}",method = RequestMethod.GET)
 public String getNewsDetails(ModelMap model, @PathVariable("newsId") Long newsId) {
     //newsEnt is null here...
     NewsEntity newsEnt = newsService.getNewsDetail(newsId);

     model.addAttribute("newsDet", newsEnt);
     return "newsdetails";
 }
}

Answer 1

您正在直接调用 mongoOperations 实例，而不是先检索集合。与您实现的 findAll 方法非常相似，您还需要包含集合作为参数的表单:

public NewsEntity getNewsDetail(Long id) {
    return mongoOperations.findOne(
        Query.query(Criteria.where("_id").is(id)),
        NewsEntity.class,
        COLLECTION_NAME
    );
}

findOne 的文档中对此进行了介绍, 另请参阅 summary 中可用的方法签名.