Java 在 Spring Data (MongoDB) 中实现 findOne
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Implementing findOne in Spring Data (MongoDB)
提问by Iurii
I have some problems with executing findOne method of MongoOperations class, for now this method return null. My data structure in mongoDB is looking like this:
我在执行 MongoOperations 类的 findOne 方法时遇到了一些问题，现在这个方法返回 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" }
As you can see above _id field has Double type. My Java classes is looking like this:
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);
}
Entity 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;
}
}
And Spring controller:
和弹簧控制器：
@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";
}
}
采纳答案by Neil Lunn
You are calling the mongoOperationsinstance directly and not first retrieving a collection. So much like the findAllmethod you have implemented you also need the form that contains the collection as an argument:
您是mongoOperations直接调用实例而不是首先检索集合。与findAll您实现的方法非常相似，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
);
}
This is covered in the documentation for findOne, also see the available method signatures in the summary.
