问题描述
我有一个名为user的类,可以简化为:
I have a class called user which can be simplified to:
class User {
String[] friends;
//Constructor etc...
}
它存储在称为用户的mongo集合中.我正在尝试从类中检索friends数组的前N个元素,而没有其他任何内容.
It is stored in a mongo collections called users. I am trying to retrieve the first N elements of the friends array without anything else from the class.
现在,我尝试使用以下Java查询:
Right now, I tried using the following java query:
db.getCollection("users").find(new BasicDBObject(), new BasicDBObject("friends", new BasicDBObject("$slice", N))).next();
正如预期的那样,我得到了一个带有friends数组切片的User对象.但是它还会返回User类中的所有其他字段(此处未显示),这是我不想要的.
As expected, I get a User object with the friends array slice. But it also returns all the other fields in the User class (not shown here), which I don't want.
有什么主意我可以强迫它只发回好友数组吗?
Any idea how I can force it to send back only the friends array?
++欢呼声
推荐答案
尝试添加"friends:true",像这样:
Try adding "friends: true" like this:
db.getCollection("users").find(new BasicDBObject(), new BasicDBObject("friends", new BasicDBObject("$slice", N)).append("friends", true)).next();
它应该具有_id和friends字段.
It should have the _id and the friends fields.
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