Use Database Commands
The MongoDB command interface provides access to all non CRUD database operations. Fetching server statistics, initializing a replica set, and running an aggregation pipeline or map-reduce job are all accomplished with commands.
See Database Commands for list of all commands sorted by function.
Database Command Form
You specify a command first by constructing a standard BSON
document whose first key is the name of the command. For example,
specify the hello command using the following
BSON document:
{ hello: 1 }
Issue Commands
The mongo shell provides a helper method for running
commands called db.runCommand(). The following operation in
mongo runs the previous command:
db.runCommand( { hello: 1 } )
Many Drivers provide an equivalent for
the db.runCommand() method. Internally, running commands
with db.runCommand() is equivalent to a special query
against the $cmd collection.
Many common commands have their own shell helpers or wrappers in the
mongo shell and drivers, such as the
db.hello() method in the mongo JavaScript
shell.
You can use the maxTimeMS option to specify a time limit for the
execution of a command, see Terminate a Command for
more information on operation termination.
admin Database Commands
You must run some commands on the admin database. Normally, these operations resemble the following:
use admin db.runCommand( {buildInfo: 1} )
However, there's also a command helper that automatically runs the
command in the context of the admin database:
db.adminCommand( {buildInfo: 1} )
Command Responses
For all commands, MongoDB returns a response document that contains the following fields:
Field | Description |
|---|---|
<command result> | Result fields specific to the command that ran. |
ok | A number that indicates if the command succeeded ( 1)
or failed (0). |
operationTime | The logical time of the performed operation, represented in MongoDB by the timestamp from the oplog entry. Only for replica sets and sharded clusters If the command does not generate an oplog entry, for example, a
read operation, then the operation does not advance the logical
clock. In this case,
For operations associated with causally consistent sessions, the MongoDB drivers use the logical time
to automatically set the Read Operations and New in version 3.6. |
$clusterTime | A document that returns the signed cluster time. Cluster time is a logical time used for ordering of operations. Only for replica sets and sharded clusters. For internal use only. The document contains the following fields:
New in version 3.6. |