November 2021
Intermediate to advanced
410 pages
12h 1m
Chinese
Content preview from MongoDB权威指南（第3版）
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48
｜
第
4
章
这既会匹配
"user_id"
等于
12345
的文档，也会匹配
"user_id"
等于
"joe"
的文档。
如果
"$in"
对应的数组只有一个值，那么和直接匹配这个值的效果是一样的。例如，
{ticket_no : {$in : [725]}}
和
{ticket_no : 725}
将匹配相同的文档。
与
"$in"
相反的是
"$nin"
，此运算符会返回与数组中所有条件都不匹配的文档。如果想返
回所有没有中奖的人，可以这样进行查询：
> db.raffle.find({"ticket_no" : {"$nin" : [725, 542, 390]}})
这条查询语句会返回所有没有这些号码的人。
"$in"
能够对单个键进行
OR
查询，但如果想找到
"ticket_no"
为
725
或者
"winner"
为
true
的文档该怎么办呢？对于这类查询，需要使用
"$or"
条件运算符。
"$or"
会接受一个
包含所有可能条件的数组作为参数。在上面的抽奖活动例子中，使用
"$or"
会是这样：
> db.raffle.find({"$or" : [{"ticket_no" : 725}, {"winner" : true}]})
"$or"
可以包含其他条件。如果希望匹配到
3
个
"ticket_no"
中的
1
个，或者
"winner"
键
的值为
true
的文档，可以这样做：
> db.raffle.find({"$or" : [{"ticket_no" : {"$in" : [725, 542, 390]}},
... {"winner" : ...
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I wanted to learn C and C++, but it didn't click for me until I picked up an O'Reilly book. When I went on the O’Reilly platform, I was astonished to find all the books there, plus live events and sandboxes so you could play around with the technology.Addison B.
I’ve been on the O’Reilly platform for more than eight years. I use a couple of learning platforms, but I'm on O'Reilly more than anybody else. When you're there, you start learning. I'm never disappointed.Amir M.
I'm always learning. So when I got on to O'Reilly, I was like a kid in a candy store. There are playlists. There are answers. There's on-demand training. It's worth its weight in gold, in terms of what it allows me to do.