Connection

You cannot connect to MongoDB by going to http://localhost:27017 in your web browser. The database cannot be accessed via HTTP on port 27017. Standard Connection String Format The uri scheme described on this page is not yet supported by all of the drivers. Refer to a specific driver's documentation to see how much (if any) of the standard connection uri is supported. All drivers support an alternative method of specifying connections if this format is not supported. mongodb://[username:password@]host1[:port1][,host2[:port2],...[,hostN[:portN]]][/[database][?options]] mongodb:// is a required prefix to identify that this is a string in the standard connection format. username:password@ are optional. If given, the driver will attempt to login to a database after connecting to a database server.//通过uri一次登录到某个数据库上时才用需要此项，若不需要上来就连到到非test数据库,则可不写。 host1 is the only required part of the URI. It identifies a server address to connect to. :portX is optional and defaults to :27017 if not provided. /database is the name of the database to login to and thus is only relevant if the username:password@ syntax is used. If not specified the "admin" database will be used by default. ?options are connection options. Note that if database is absent (指不显示指定时)there is still a / required between the last host and the ?introducing the options. Options are name=value pairs and the pairs are separated either by "&"" or ";". A database consists of one or more collections, the documents (objects) in those collections, and an optional set of security credentials(证书) for controlling access. As many hosts as necessary may be specified (for connecting to replica pairs/sets,2个副本（其实没有真本）叫pair,多余2个副本 叫 set).//数据库或option共用一个，因为多台机子应相同 The options are: Replica set: replicaSet=name The driver verifies that the name of the replica set it connects to matches this name. Implies that the hosts given are a seed list, and the driver will attempt to find all members of the set. Single server: slaveOk=true|false Any configuration: safe=true|false true: the driver sends a getLastError command after every update to ensure that the update succeeded (see also w andwtimeoutMS). false: the driver does not send a getLastError command after every update. w=n The driver adds { w : n } to the getLastError command. Implies safe=true. wtimeoutMS=ms The driver adds { wtimeout : ms } to the getlasterror command. Implies safe=true. fsync=true|false true: the driver adds { fsync : true } to the getlasterror command. Implies safe=true. false: the driver does not not add fsync to the getlasterror command. journal=true|false true: Sync to journal. Implies safe=true. connectTimeoutMS=ms How long a connection can take to be opened before timing out. socketTimeoutMS=ms How long a send or receive on a socket can take before timing out. These options are not case sensitive. Examples Connect to a database server running locally on the default port: mongodb://localhost Connect and login to the admin database as user "fred" with password "foobar": mongodb://fred:foobar@localhost Connect and login to the "baz" database as user "fred" with password "foobar": mongodb://fred:foobar@localhost/baz Connect to a replica pair, with one server on example1.com and another server on example2.com: mongodb://example1.com:27017,example2.com:27017 Connect to a replica set with three servers running on localhost (on ports 27017, 27018, and 27019): mongodb://localhost,localhost:27018,localhost:27019 Connect to a replica set with three servers, sending all writes to the primary and distributing reads to the secondaries: mongodb://host1,host2,host3/?slaveOk=true Connect to localhost with safe mode on: mongodb://localhost/?safe=true Connect to a replica set with safe mode on, waiting for replication to succeed on at least two machines, with a two second timeout: mongodb://host1,host2,host3/?safe=true;w=2;wtimeoutMS=2000 Connection Pooling   The server will use one thread per TCP connection, therefore it is highly recomended that your application use some sort of connection pooling ？？？？. Luckily, most drivers handle this for you behind the scenes. One notable exception is setups where your app spawns a new process for each request, such as CGI and some configurations of PHP.