MongoDB自学笔记8--- 3.3 MongoDB Shell简介及简单使用(二)
"name" : "user2", "age" : 12 }
find方法一般会接收一个BSON对象作为参数，如果没有传参数，默认也就是一个空的BSON对象，意思是查出所有的文档。如下就是查出了user集合中的所有对象：
> db.user.find()
{ "_id" : ObjectId("519cbddfe9c1b21d76cc927c"), "name" : "xiangyue", "age" : 23 }
{ "_id" : 1, "name" : "user1", "age" : 11 }
{ "_id" : 2, "name" : "user2", "age" : 12 }
{ "_id" : 3, "name" : "user3", "age" : 13 }
{ "_id" : 4, "name" : "user4", "age" : 14 }
{ "_id" : 5, "name" : "user5", "age" : 15 }
{ "_id" : 6, "name" : "user6", "age" : 16 }
{ "_id" : 7, "name" : "user7", "age" : 17 }
{ "_id" : 8, "name" : "user8", "age" : 18 }
{ "_id" : 9, "name" : "user9", "age" : 19 }
{ "_id" : 10, "name" : "user10", "age" : 20 }
3.3.7 删除数据
在mongodb中删除数据，使用remove，这个方法的使用方法与find类似，只是find是查找出来满足条件的，remove是删除满足条件的。
我们还是利用上面的数据，删除name为user2的用户，代码如下：
> db.user.find()
{ "_id" : 1, "name" : "user1", "age" : 11 }
{ "_id" : 2, "name" : "user2", "age" : 12 }
{ "_id" : 3, "name" : "user3", "age" : 13 }
{ "_id" : 4, "name" : "user4", "age" : 14 }
{ "_id" : 5, "name" : "user5", "age" : 15 }
{ "_id" : 6, "name" : "user6", "age" : 16 }
{ "_id" : 7, "name" : "user7", "age" : 17 }
{ "_id" : 8, "name" : "user8", "age" : 18 }
{ "_id" : 9, "name" : "user9", "age" : 19 }
{ "_id" : 10, "name" : "user10", "age" : 20 }
> db.user.remove({name:"user2"})
> db.user.find()
{ "_id" : 1, "name" : "user1", "age" : 11 }
{ "_id" : 3, "name" : "user3", "age" : 13 }
{ "_id" : 4, "name" : "user4", "age" : 14 }
{ "_id" : 5, "name" : "user5", "age" : 15 }
{ "_id" : 6, "name" : "user6", "age" : 16 }
{ "_id" : 7, "name" : "user7", "age" : 17 }
{ "_id" : 8, "name" : "user8", "age" : 18 }
{ "_id" : 9, "name" : "user9", "age" : 19 }
{ "_id" : 10, "name" : "user10", "age" : 20 }
3.3.8 更新数据
更新数据需要使用update操作。我们将name为user3的用户改为user33。
> db.user.find()
{ "_id" : 1, "name" : "user1", "age" : 11 }
{ "_id" : 3, "name" : "user3", "age" : 13 }
{ "_id" : 4, "name" : "user4", "age" : 14 }
{ "_id" : 5, "name" : "user5", "age" : 15 }
{ "_id" : 6, "name" : "user6", "age" : 16 }
{ "_id" : 7, "name" : "user7", "age" : 17 }
{ "_id" : 8, "name" : "user8", "age" : 18 }
{ "_id" : 9, "name" : "user9", "age" : 19 }
{ "_id" : 10, "name" : "user10", "age" : 20 }
> db.user.update({name:"user3"},{_id:3,name:"user33",age:13})
> db.user.find()
{ "_id" : 1, "name" : "user1", "age" : 11 }
{ "_id" : 3, "name" : "user33", "age" : 13 }
{ "_id" : 4, "name" : "user4", "age" : 14 }
{ "_id" : 5, "name" : "user5", "age" : 15 }
{ "_id" : 6, "name" : "user6", "age" : 16 }
{ "_id" : 7, "name" : "user7", "age" : 17 }
{ "_id" : 8, "name" : "user8", "age" : 18 }
{ "_id" : 9, "name" : "user9", "age" : 19 }
{ "_id" : 10, "name" : "user10", "age" : 20 }
3.3.9 help()使用
Mongodb为我们提供了很好的帮助，我们可以使用类似如下的命令查看数据库的帮助和集合的帮助：
db.help() /*查看数据库的帮助，该方法显示数据库级能使用的方法*/
db.[集合名].help() /*查看集合的帮助，该方法显示集合级能使用的方法*/