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MongoDB: 1. Database

mongo 是 MongoDB 自带的交互式 Javascript shell,用来对 Mongod 进行操作和管理的交互式环境。

使用 "./mongo --help" 可查看相关连接参数。
$ ./mongo --help

MongoDB shell version: 1.5.3

usage: ./mongo [options] [db address] [file names (ending in .js)]

db address can be:
  foo                   foo database on local machine
  192.169.0.5/foo       foo database on 192.168.0.5 machine
  192.169.0.5:9999/foo  foo database on 192.168.0.5 machine on port 9999

options:
  --shell               run the shell after executing files
  --nodb                don't connect to mongod on startup - no 'db address'
                        arg expected
  --quiet               be less chatty
  --port arg            port to connect to
  --host arg            server to connect to
  --eval arg            evaluate javascript
  -u [ --username ] arg username for authentication
  -p [ --password ] arg password for authentication
  -h [ --help ]         show this usage information
  --version             show version information
  --ipv6                enable IPv6 support (disabled by default)

file names: a list of files to run. files have to end in .js and will exit after unless --shell is specified

相关命令很多,要习惯使用 "help"。
$ ./mongo

MongoDB shell version: 1.5.3
connecting to: test
type "help" for help

> help
        help admin                   misc shell commands
        show dbs                     show database names
        show collections             show collections in current database
        show users                   show users in current database
        show profile                 show most recent system.profile entries with time >= 1ms
        use <db name>                set current database to <db name>
        db.help()                    help on DB methods
        db.foo.help()                help on collection methods
        db.foo.find()                list objects in collection foo
        db.foo.find( { a : 1 } )     list objects in foo where a == 1
        it                           result of the last line evaluated; use to further iterate
        exit                         quit the mongo shell

(1) MongoDB 会自动创建数据库(db)和集合(collection),无需显式执行。
$ ./mongo

MongoDB shell version: 1.5.3
connecting to: test
type "help" for help

> show dbs // 查看当前数据库列表
admin
local

> use blog // 切换到工作数据库
switched to db blog

> db // 当前数据库
blog

> for (var i = 0; i < 10; i++) db.users.save({name : "user" + i, age : i}) // 插入数据

> show dbs // 数据库 blog 被创建
admin
blog
local

> show collections // 列表 users 被创建
system.indexes
users

> db.copyDatabase("blog", "blog2") // 复制数据库
{ "ok" : true }

> show dbs // 数据库 blog2 被创建
admin
blog
blog2
local

> use blog2 // 切换到 blog2
switched to db blog2

> show collections // 查看集合列表
system.indexes
users

> db.users.find() // 查看被复制的数据
{ "_id" : ObjectId("4c33f8fcecf2b9320ac2981a"), "name" : "user0", "age" : 0 }
{ "_id" : ObjectId("4c33f8fcecf2b9320ac2981b"), "name" : "user1", "age" : 1 }
{ "_id" : ObjectId("4c33f8fcecf2b9320ac2981c"), "name" : "user2", "age" : 2 }
{ "_id" : ObjectId("4c33f8fcecf2b9320ac2981d"), "name" : "user3", "age" : 3 }
{ "_id" : ObjectId("4c33f8fcecf2b9320ac2981e"), "name" : "user4", "age" : 4 }
{ "_id" : ObjectId("4c33f8fcecf2b9320ac2981f"), "name" : "user5", "age" : 5 }
{ "_id" : ObjectId("4c33f8fcecf2b9320ac29820"), "name" : "user6", "age" : 6 }
{ "_id" : ObjectId("4c33f8fcecf2b9320ac29821"), "name" : "user7", "age" : 7 }
{ "_id" : ObjectId("4c33f8fcecf2b9320ac29822"), "name" : "user8", "age" : 8 }
{ "_id" : ObjectId("4c33f8fcecf2b9320ac29823"), "name" : "user9", "age" : 9 }

> db.dropDatabase() // 删除数据库 blog2
{ "dropped" : "blog2", "ok" : true }

> show dbs // 确认数据库删除成功
admin
blog
local

> use blog // 切换回 blog
switched to db blog

> db.users.drop()  // 删除集合 users
true

> show collections // 确认集合被删除
system.indexes

> exit
bye

(2) 还可以在多台服务器之间复制数据库。
server64$ ./mongo

MongoDB shell version: 1.5.3
connecting to: test
type "help" for help

> use blog
switched to db blog

> for (var i = 0; i < 10; i++) db.users.save({name : "user" + i, age : i})

> use news
switched to db news

> for (var i = 0; i < 10; i++) db.articles.save({title : "title" + i})

> show dbs
admin
blog
local
news

> exit
bye

准备好源数据库后,我们开始在复制。
server32:$ ./mongo

MongoDB shell version: 1.5.4
connecting to: test

> db.copyDatabase("blog", "blog", "192.168.1.202") // 从源服务器复制 blog 数据库
{ "ok" : true }

> show dbs // 复制成功
admin
blog
local

> use blog
switched to db blog

> show collections
system.indexes
users

> db.users.find()
{ "_id" : ObjectId("4c33fadb15b7f104d297e644"), "name" : "user0", "age" : 0 }
{ "_id" : ObjectId("4c33fadb15b7f104d297e645"), "name" : "user1", "age" : 1 }
{ "_id" : ObjectId("4c33fadb15b7f104d297e646"), "name" : "user2", "age" : 2 }
{ "_id" : ObjectId("4c33fadb15b7f104d297e647"), "name" : "user3", "age" : 3 }
{ "_id" : ObjectId("4c33fadb15b7f104d297e648"), "name" : "user4", "age" : 4 }
{ "_id" : ObjectId("4c33fadb15b7f104d297e649"), "name" : "user5", "age" : 5 }
{ "_id" : ObjectId("4c33fadb15b7f104d297e64a"), "name" : "user6", "age" : 6 }
{ "_id" : ObjectId("4c33fadb15b7f104d297e64b"), "name" : "user7", "age" : 7 }
{ "_id" : ObjectId("4c33fadb15b7f104d297e64c"), "name" : "user8", "age" : 8 }
{ "_id" : ObjectId("4c33fadb15b7f104d297e64d"), "name" : "user9", "age" : 9 }

> use news
switched to db news

> db.cloneDatabase("192.168.1.202") // 从源服务器克隆当前数据库(news)
{ "ok" : true }

> show dbs
admin
blog
local
news

> show collections
articles
system.indexes

> db.articles.find()
{ "_id" : ObjectId("4c33fb6215b7f104d297e64e"), "title" : "title0" }
{ "_id" : ObjectId("4c33fb6215b7f104d297e64f"), "title" : "title1" }
{ "_id" : ObjectId("4c33fb6215b7f104d297e650"), "title" : "title2" }
{ "_id" : ObjectId("4c33fb6215b7f104d297e651"), "title" : "title3" }
{ "_id" : ObjectId("4c33fb6215b7f104d297e652"), "title" : "title4" }
{ "_id" : ObjectId("4c33fb6215b7f104d297e653"), "title" : "title5" }
{ "_id" : ObjectId("4c33fb6215b7f104d297e654"), "title" : "title6" }
{ "_id" : ObjectId("4c33fb6215b7f104d297e655"), "title" : "title7" }
{ "_id" : ObjectId("4c33fb6215b7f104d297e656"), "title" : "title8" }
{ "_id" : ObjectId("4c33fb6215b7f104d297e657"), "title" : "title9" }

> exit
bye

(3) 当我们使用 use 切换到某个数据库时,变量 db 表示当前数据库。还可以用 getSisterDB() 函数获取其他数据库的引用。
> use admin
switched to db admin

> db
admin

> blog = db.getSisterDB("blog")
blog

> blog.users.insert({name : "abc"})

> blog.users.find({name : "abc"})
{ "_id" : ObjectId("4c3419b0492aa4cfbec11895"), "name" : "abc" }

(4) 调用 fsync 命令,可以强制将内存中缓存数据写回数据库文件。如果不想等待,可添加 async 参数异步执行。
> use admin
switched to db admin

> db.runCommand({fsync : 1})
{ "numFiles" : 6, "ok" : true }

> db.runCommand({fsync : 1, async : true})
{ "numFiles" : 6, "ok" : true }

(5) 某些时候需要锁定系统,阻塞所有写操作,诸如备份、整理数据库等等。锁定时读操作不受影响。
$ ./mongo

MongoDB shell version: 1.5.3
connecting to: test
type "help" for help

> use blog
switched to db blog

> admin = db.getSisterDB("admin")
admin

> admin.runCommand({fsync : 1, lock : 1}) // 锁定
{
        "info" : "now locked against writes, use db.$cmd.sys.unlock.findOne() to unlock",
        "ok" : true
}

> db.users.find() // 读操作正常

{ "_id" : ObjectId("4c33fadb15b7f104d297e644"), "name" : "user0", "age" : 0 }
{ "_id" : ObjectId("4c33fadb15b7f104d297e645"), "name" : "user1", "age" : 1 }
{ "_id" : ObjectId("4c33fadb15b7f104d297e646"), "name" : "user2", "age" : 2 }
{ "_id" : ObjectId("4c33fadb15b7f104d297e647"), "name" : "user3", "age" : 3 }
{ "_id" : ObjectId("4c33fadb15b7f104d297e648"), "name" : "user4", "age" : 4 }
{ "_id" : ObjectId("4c33fadb15b7f104d297e649"), "name" : "user5", "age" : 5 }
{ "_id" : ObjectId("4c33fadb15b7f104d297e64a"), "name" : "user6", "age" : 6 }
{ "_id" : ObjectId("4c33fadb15b7f104d297e64b"), "name" : "user7", "age" : 7 }
{ "_id" : ObjectId("4c33fadb15b7f104d297e64c"), "name" : "user8", "age" : 8 }
{ "_id" : ObjectId("4c33fadb15b7f104d297e64d"), "name" : "user9", "age" : 9 }

> db.users.save({name : "xyz" }) // 写操作被阻塞,等待 ...

另开启一个终端,解除锁定。
> use admin
switched to db admin

> db.$cmd.sys.unlock.findOne()
{ "ok" : 1, "info" : "unlock requested" }

解除后,前一终端被阻塞的写操作正确返回。
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