Befehle

Introduction

The Mongo database has a concept of a database command. Database commands are ways to ask the database to perform special operations, or to request information about its current operational status.

• [List of Database Commands]

A command is sent to the database as a query to a special collection namespace called $cmd. The database will return a single document with the command results - use findOne() for that if your driver has it.

The general command syntax is:

db.$cmd.findOne( { <commandname>: <value> [, options] } ); 

The shell provides a helper function for this:

db.runCommand( { <commandname>: <value> [, options] } ); 

For example, to check our database's current profile level setting, we can invoke:

> db.runCommand({profile:-1}); 
{ 
"was" : 0.0 , 
"ok" : 1.0 
} 

For many db commands, some drivers implement wrapper methods are implemented to make usage easier. For example, the [mongo shell ] offers

> db.getProfilingLevel() 
0.0 

Let's look at what this method is doing:

> print( db.getProfilingLevel ) 
function () { 
var res = this._dbCommand({profile:-1}); 
return res ? res.was : null; 
} 

> print( db._dbCommand ) 
function (cmdObj) { 
return this.$cmd.findOne(cmdObj); 
} 

Many commands have helper functions - see your driver's documentation for more information.

Privileged Commands

Certain operations are for the database administrator only. These privileged operations may only be performed on the special database named admin.

> use admin; 
> db.runCommand("shutdown"); // shut down the database 

If the db variable is not set to 'admin', you can use _adminCommand to switch to the right database automatically (and just for that operation):

> db._adminCommand("shutdown"); 

(For this particular command there is also a shell helper function, db.shutdownServer.)

Getting Help Info for a Command

Use commandHelp in shell to get help info for a command:

> db.commandHelp("datasize") 
help for: datasize example: { datasize:"blog.posts", keyPattern:{x:1}, min:{x:10}, max:{x:55} } 
NOTE: This command may take awhile to run 

(Help is not yet available for some commands.)

More Command Documentation

• "Last Error" Befehle
• Beobachten und Beenden laufender Vorgänge
• Datenbank klonen
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• Index bezogene Befehle
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• Validieren
• Windows Service