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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112
第 6 章
特殊的索引和集合类型
本章介绍
MongoDB
中的一些特殊的索引和集合类型，包括：
•
用于类队列数据的固定集合（
capped collection
）；
•
用于缓存的
TTL
索引；
•
用于简单字符串搜索的全文本索引；
•
用于二维平面和球体空间的地理空间索引；
•
用于存储大文件的
GridFS
。
6.1
地理空间索引
MongoDB
有两种类型的地理空间索引：
2dsphere
和
2d
。
2dsphere
索引可以与基于
WGS84
基准的地球球面几何模型一起使用。这个基准将地球表面模拟成一个扁圆球体，这意味着
在两极会比较扁。因此，使用
2dsphere
索引的距离计算考虑到了地球的形状，提供了比
2d
索引更准确的距离处理，比如计算两个城市之间的距离。在存储二维平面上的点时使用
2d
索引。
2dsphere
允许以
GeoJSON
格式指定点、线和多边形这些几何图形。一个点由一个二元数
组给出，表示
[
经度
,
纬度
]
（
[
longitude
,
latitude
]
）：
{
"name" : "New York City",
"loc" : {
"type" : "Point",
"coordinates" : [50, 2]
}
}
特殊的索引和集合类型
｜
113
线可以用一个由点组成的数组来表示：
{
"name" ...
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