MongoDB中集合ID的长度 [英] Collection ID length in MongoDB

问题描述

我是mongodb的新手，并且堆栈溢出.

i am new to mongodb and stack overflow.

我想知道为什么在mongodb上ID为24个十六进制字符? 这有什么重要性?

I want to know why on mongodb collection ID is of 24 hex characters? what is importance of that?

推荐答案

为什么默认的_id是24个字符的十六进制字符串?

作为MongoDB文档的主键(_id)生成的默认唯一标识符是 ObjectId .这是一个12字节的二进制值，通常表示为24个字符的十六进制字符串，并且是MongoDB支持的标准字段类型之一 BSON规范.

Why is the default _id a 24 character hex string?

The default unique identifier generated as the primary key (_id) for a MongoDB document is an ObjectId. This is a 12 byte binary value which is often represented as a 24 character hex string, and one of the standard field types supported by the MongoDB BSON specification.

ObjectId的12个字节的构造方法是:

The 12 bytes of an ObjectId are constructed using:

• 一个4字节的值，表示自Unix时代以来的秒数
• 3字节机器标识符
• 一个2字节的进程ID
• 3字节计数器(以随机值开头)

ObjectId(或根据 GUID 公式生成的类似标识符)允许在分布式系统中独立生成唯一标识符

ObjectIds (or similar identifiers generated according to a GUID formula) allow unique identifiers to be independently generated in a distributed system.

当您扩展到多个应用程序服务器(或者

The ability to independently generate a unique ID becomes very important as you scale up to multiple application servers (or perhaps multiple database nodes in a sharded cluster). You do not want to have a central coordination bottleneck like a sequence counter (eg. as you might have for an auto-incrementing primary key), and you will want to insert new documents without risk that a new identifier will turn out to be a duplicate.

ObjectId通常是由您的MongoDB 客户端驱动程序生成的，但如果您的MongoDB服务器客户端驱动程序或应用程序代码，或者尚未添加_id字段.

An ObjectId is typically generated by your MongoDB client driver, but can also be generated on the MongoDB server if your client driver or application code or haven't already added an _id field.

不.如果您有更适合使用的唯一标识符，则始终可以为_id提供自己的值.它可以是单个值，也可以是使用多个字段的复合值.

No. If you have a more suitable unique identifier to use, you can always provide your own value for _id. This can either be a single value or a composite value using multiple fields.

_id值的主要限制是它们对于集合必须是唯一的，并且您不能更新或删除现有文档的_id.

The main constraints on _id values are that they have to be unique for a collection and you cannot update or remove the _id for an existing document.

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