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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入门指南
｜
13
可以看到输入的键
–
值对都完整地保存了下来，并额外添加了一个
"_id"
键。本章的最后
会解释
"_id"
字段突然出现的原因。
2.
读取
find
和
findOne
方法可用于查询集合中的文档。如果只想查看一个文档，可以使用
findOne
：
> db.movies.findOne()
{
"_id" : ObjectId("5721794b349c32b32a012b11"),
"title" : "Star Wars: Episode IV - A New Hope",
"director" : "George Lucas",
"year" : 1977
}
find
和
findOne
也可以接受一个查询文档作为限定条件。这样就可以限制查询匹配到的
文档了。使用
find
时，
shell
将自动显示最多
20
个匹配的文档，但也可以获取更多文档。
（有关查询的详细信息，请参阅第
4
章
。）
3.
更新
如果想修改文档，可以使用
updateOne
。
updateOne
会接受（至少）两个参数：第一个用于
查找要更新文档的限定条件，第二个用于描述要进行更新的文档。假设我们决定为先前创
建的电影启用评论功能，那么就需要在文档中添加一个新的键，用于保存评论的数组。
要执行更新，需要使用更新运算符
set
：
> db.movies.updateOne({title : "Star Wars: Episode IV - A New Hope"},
... {$set : {reviews: []}})
WriteResult({"nMatched": ...
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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.