MongoDB是一個NoSQL資料庫系統：一個資料庫可以包含多個集合（Collection），每個集合對應於關聯式資料庫中的表；而每個集合中可以儲存一組由列標識的記錄，列是可以自由定義的，非常靈活，由一組列標識的實體的集合對應於關聯式資料庫表中的行。下面通過熟悉MongoDB的基本管理命令，來瞭解MongoDB提供的DBMS的準系統和行為。
MongoDB命令協助系統
在安裝MongoDB後，啟動伺服器處理序（mongod），可以通過在用戶端命令mongo實現對MongoDB的管理和監控。看一下MongoDB的命令協助系統：
- root@dev2:~# mongo
- MongoDB shell version: 1.8.3
- connecting to: test
- > help
- db.help() help on db methods
- db.mycoll.help() help on collection methods
- rs.help() help on replica set methods
- help connect connecting to a db help
- help admin administrative help
- help misc misc things to know
- help mr mapreduce help
-
- 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
- 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
- DBQuery.shellBatchSize = x set default number of items to display on shell
- exit quit the mongo shell
這是MongoDB最頂層的命令列表，主要告訴我們管理資料庫相關的一些抽象的範疇：資料庫操作協助、集合操作協助、管理協助。如果你想瞭解資料庫操作更詳細的協助命令，可以直接使用db.help()，如下所示：
- > db.help()
- DB methods:
- db.addUser(username, password[, readOnly=false])
- db.auth(username, password)
- db.cloneDatabase(fromhost)
- db.commandHelp(name) returns the help for the command
- db.copyDatabase(fromdb, todb, fromhost)
- db.createCollection(name, { size : ..., capped : ..., max : ... } )
- db.currentOp() displays the current operation in the db
- db.dropDatabase()
- db.eval(func, args) run code server-side
- db.getCollection(cname) same as db['cname'] or db.cname
- db.getCollectionNames()
- db.getLastError() - just returns the err msg string
- db.getLastErrorObj() - return full status object
- db.getMongo() get the server connection object
- db.getMongo().setSlaveOk() allow this connection to read from the nonmaster member of a replica pair
- db.getName()
- db.getPrevError()
- db.getProfilingLevel() - deprecated
- db.getProfilingStatus() - returns if profiling is on and slow threshold
- db.getReplicationInfo()
- db.getSiblingDB(name) get the db at the same server as this one
- db.isMaster() check replica primary status
- db.killOp(opid) kills the current operation in the db
- db.listCommands() lists all the db commands
- db.printCollectionStats()
- db.printReplicationInfo()
- db.printSlaveReplicationInfo()
- db.printShardingStatus()
- db.removeUser(username)
- db.repairDatabase()
- db.resetError()
- db.runCommand(cmdObj) run a database command. if cmdObj is a string, turns it into { cmdObj : 1 }
- db.serverStatus()
- db.setProfilingLevel(level,<slowms>) 0=off 1=slow 2=all
- db.shutdownServer()
- db.stats()
- db.version() current version of the server
- db.getMongo().setSlaveOk() allow queries on a replication slave server
對資料庫進行管理和操作的基本命令，可以從上面擷取到。如果想要得到更多，而且每個命令的詳細用法，可以使用上面列出的db.listCommands()查詢。
另一個比較基礎的是對指定資料庫的集合進行操作、管理和監控，可以通過查詢db.mycoll.help()擷取到：
- > db.mycoll.help()
- DBCollection help
- db.mycoll.find().help() - show DBCursor help
- db.mycoll.count()
- db.mycoll.dataSize()
- db.mycoll.distinct( key ) - eg. db.mycoll.distinct( 'x' )
- db.mycoll.drop() drop the collection
- db.mycoll.dropIndex(name)
- db.mycoll.dropIndexes()
- db.mycoll.ensureIndex(keypattern[,options]) - options is an object with these possible fields: name, unique, dropDups
- db.mycoll.reIndex()
- db.mycoll.find([query],[fields]) - query is an optional query filter. fields is optional set of fields to return.
- e.g. db.mycoll.find( {x:77} , {name:1, x:1} )
- db.mycoll.find(...).count()
- db.mycoll.find(...).limit(n)
- db.mycoll.find(...).skip(n)
- db.mycoll.find(...).sort(...)
- db.mycoll.findOne([query])
- db.mycoll.findAndModify( { update : ... , remove : bool [, query: {}, sort: {}, 'new': false] } )
- db.mycoll.getDB() get DB object associated with collection
- db.mycoll.getIndexes()
- db.mycoll.group( { key : ..., initial: ..., reduce : ...[, cond: ...] } )
- db.mycoll.mapReduce( mapFunction , reduceFunction , <optional params> )
- db.mycoll.remove(query)
- db.mycoll.renameCollection( newName , <dropTarget> ) renames the collection.
- db.mycoll.runCommand( name , <options> ) runs a db command with the given name where the first param is the collection name
- db.mycoll.save(obj)
- db.mycoll.stats()
- db.mycoll.storageSize() - includes free space allocated to this collection
- db.mycoll.totalIndexSize() - size in bytes of all the indexes
- db.mycoll.totalSize() - storage allocated for all data and indexes
- db.mycoll.update(query, object[, upsert_bool, multi_bool])
- db.mycoll.validate() - SLOW
- db.mycoll.getShardVersion() - only for use with sharding
有關資料庫和集合管理的相關命令，是最基礎和最常用的，如集合查詢、索引操作等。
