流星如何在客户端创建唯一的MongoDB _id? [英] How does Meteor create a unique MongoDB _id on the client side?
问题描述
根据流星文档关于Mongo.Collection.insert()函数的信息，
插入将为您传递的对象生成一个唯一的ID，将其插入数据库中，然后返回ID.
insert will generate a unique ID for the object you pass, insert it in the database, and return the ID.
它也可以异步工作:
如果提供回调，insert仍会立即返回ID.
If you do provide a callback, insert still returns the ID immediately.
是否可以保证所生成的_id是全局唯一的?流星的Minimongo如何在客户端生成这样的_id?
Is there any guarantee that the generated _id is globally unique? How does Meteor's Minimongo generate such an _id on the client side?
推荐答案
由于Meteor是开源的，因此您可以确切地看到它是如何完成的.
As Meteor is open source you can see exactly how this is done.
- README for random package
- random.js
自述文件:
random软件包提供了几种用于生成随机数的功能 数字.它使用密码学上强的伪随机数 生成器(如果可能)，但回退到较弱的随机数 密码强随机性不可用时的生成器 (在较旧的浏览器或没有足够熵的服务器上 播种加密强度高的生成器).
The random package provides several functions for generating random numbers. It uses a cryptographically strong pseudorandom number generator when possible, but falls back to a weaker random number generator when cryptographically strong randomness is not available (on older browsers or on servers that don't have enough entropy to seed the cryptographically strong generator).
Random.id([n])-返回唯一标识符，例如
"Jjwjg6gouWLXhMGKW"，在全世界很可能是唯一的.
可选参数n指定标识符的长度
字符，默认为17.
Random.id([n]) - Returns a unique identifier, such as
"Jjwjg6gouWLXhMGKW", that is likely to be unique in the whole world.
The optional argument n specifies the length of the identifier in
characters and defaults to 17.
简短的答案是，流星使用加密技术(根据@Kyll，又名数学)生成一个随机ID，该ID在全球所有mongo数据库中的所有对象之间应是全局唯一的. 运气"部分是，两个对象最终具有相同id的可能性很小.现在_id键在mongo中被索引为唯一，因此如果存在重复，则插入将失败.我怀疑Meteor可以通过错误处理来解决这种可能性.
The short answer is that Meteor uses cryptography (aka maths as per @Kyll) to generate a random id that should be globally unique across all objects in all mongo databases everywhere. The "luck" part is that there is a small chance that two objects could end up with the same id. Now the _id key is indexed unique in mongo so an insert would fail if there is a dupe. I suspect Meteor has error handling to deal with that possibility.
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