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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6
第 2 章
入门指南
MongoDB
功能强大且易于上手。本章介绍
MongoDB
的一些基本概念。
•
文档
是
MongoDB
中的基本数据单元
，可以粗略地认为其相当于关系数据库管理系统中
的行（但表达力要强得多）。
•
类似地，
集合
可以被看作具有动态模式的表。
•
一个
MongoDB
实例可以拥有多个独立的
数据库
，每个数据库都拥有自己的集合。
•
每个文档都有一个特殊的键
"_id"
，其在所属的集合中是唯一的。
• MongoDB
自带了一个简单但功能强大的工具
：
mongo shell
。
mongo shell
对管理
MongoDB
实例和使用
MongoDB
的查询语言操作数据提供了内置的支持
。它也是一个功能齐全的
JavaScript
解释器，用户可以根据需求创建或加载自己的脚本。
2.1
文档
文档
是
MongoDB
的
核心概念：它是一组有序键值的集合。文档的表示形式因编程语言
而异，但大多数语言具有自然匹配的数据结构，比如映射、哈希表或字典。例如，在
JavaScript
中，文档表示为对象：
{"greeting" : "Hello, world!"}
这个简单的文档只包含一个键，即
"greeting"
，对应的值为
"Hello, world!"
。大多数文档
会比这个例子更复杂，并且通常会包含多个键
–
值对：
{"greeting" : "Hello, world!", "views" : 3}
如上所示，文档中的值不仅仅是“二进制大对象”，它们可以是几种不同的数据类型之一
（甚至可以是一个完整的嵌入文档，请参阅
2.6.4
节）
。在本例中 ...
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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.