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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30
｜
第
3
章
删除文档的操作通常会比较快。不过，如果想清空整个集合，那么使用
drop
直接删除集
合，然后在这个空集合中重建各项索引会更快：
> db.movies.drop()
true
数据删除是永久性的。没有任何方法可以撤回删除文档或者删除集合的操作，也无法恢复
被删除的文档，当然从以前的备份中恢复除外。关于
MongoDB
备份和
恢复的详细内容，
请参阅第
23
章。
3.3
更新文档
将文档存入数据库中之后，可以使用以下几种更新方法之一对其进行更改：
updateOne
、
updateMany
和
replaceOne
。
updateOne
和
updateMany
都将筛选文档作为第一个参数，将变
更文档作为第二个参数，后者对要进行的更改进行描述。
replaceOne
同样将筛选文档作为
第一个参数，但第二个参数是一个用来替换所匹配的筛选文档的新文档。
更新文档是原子操作：如果两个更新同时发生，那么首先到达服务器的更新会先被执行，
然后再执行下一个更新。因此，相互冲突的更新可以安全地迅速接连完成，而不会破坏任
何文档：最后一次更新将“成功”。如果不想使用默认行为，则可以考虑使用文档版本控
制模式（详情请参阅
9.1
节
）。
3.3.1
文档替换
replaceOne
会用新文档完全替换匹配的文档。这对于进行大规模模式迁移（参见第
9
章）
的场景非常有用。假设要对下面的用户文档进行比较大的更改：
{
"_id" : ObjectId("4b2b9f67a1f631733d917a7a"),
"name" : "joe",
"friends" ...
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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.