Home Database Mysql Tutorial MongoDB创建集合命令db.createCollection详解

MongoDB创建集合命令db.createCollection详解

Jun 07, 2016 pm 05:34 PM
mongodb

MongoDB创建集合命令db.createCollection详解

完整的命令如下:
db.createCollection(name, {capped: , autoIndexId: , size: , max } )


name:集合的名字
capped:是否启用集合限制,如果开启需要制定一个限制条件,默认为不启用,这个参数没有实际意义
size:限制集合使用空间的大小,默认为没有限制
max:集合中最大条数限制,默认为没有限制
autoIndexId:是否使用_id作为索引,默认为使用(true或false)
size的优先级比max要高


常用方法介绍:
1、一般来说,我们创建集合用db.createCollection(name),如:db.createCollection("log"),创建一个名字为log的集合,没有任何的大小,数量限制,使用_id作为默认索引;

2、限制集合空间的大小:db.createCollection("log",{size:1024})或db.createCollection("log",{capped:true,size:1024}),创建一个名字为log集合,限制它的空间大小为1M,如果超过1M的大小,则会删除最早的记录;
3、限制集合的最大条数:db.createCollection("log",{max:1024}),创建一个名字为log集合,最大条数为1024条,超过1024再插入数据的话会删除最早的一条记录。这个不能使用capped:true,否则会报错;
4、即限制最大条数有限制使用空间大小:db.createCollection("log",{size:1024,max:1024})或db.createCollection("log",{capped:true,size:1024,max:1024}),,限制集合最大使用空间为1M,最大条数为1024条

以上是参考官方文档和实际测试得出的,也可以看出capped参数没有什么用处,用不用都可以。

MongoDB 的详细介绍:请点这里
MongoDB 的下载地址:请点这里

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