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PHP Library Manual

Run a Database Command

On this page

  • Overview
  • Execute a Command
  • Response
  • Command Example
  • Additional Information
  • API Documentation

Overview

In this guide, you can learn how to use the MongoDB PHP Library to run a database command. You can use database commands to perform a variety of administrative and diagnostic tasks, such as fetching server statistics, initializing a replica set, or running an aggregation pipeline.

Important

Prefer Library Methods to Database Commands

The library provides wrapper methods for many database commands. We recommend using these methods instead of executing database commands when possible.

To perform administrative tasks, use the MongoDB Shell instead of the MongoDB PHP Library. The shell provides helper methods that might not be available in the library.

If there are no available helpers in the library or the shell, you can use the db.runCommand() shell method or the library's MongoDB\Database::command() method, which is described in this guide.

Execute a Command

To run a database command, you must specify the command and any relevant parameters in a command document, then pass the command document to the MongoDB\Database::command() method. Many database commands return multiple result documents, so the command() method returns a MongoDB\Driver\Cursor object that you can iterate through.

The following code shows how you can use the command() method on a MongoDB\Database instance to run the hello command, which returns information about the server:

$database = $client->selectDatabase('myDB');
$cursor = $database->command(['hello' => 1]);

To find a link to a full list of database commands and corresponding parameters, see the Additional Information section.

Note

Read Preference

The command() method does not inherit the read preference you might have set on your Database instance elsewhere in your code. By default, command() uses the primary read preference.

You can set a read preference for command execution by setting one in the options parameter, as shown in the following code:

$readPref = new MongoDB\Driver\ReadPreference('primaryPreferred');
$cursor = $database->command(
    ['hello' => 1], 
    ['readPreference' => $readPref]
);

Learn more about the ReadPreference class in the PHP extension API documentation.

To learn more about read preference options, see Read Preference in the MongoDB Server manual.

Response

The command() method returns a Cursor object that contains the response from the database for the given command. Each database command performs a different function, so the response content can vary.

For commands that return a single result document, that result is available as the first and only document in the cursor. For commands that return multiple result documents, the library converts the cursor envelope in the raw command response, which includes the cursor ID and the first batch of results, into an iterable cursor.

Before you run a command, learn about the response format of the command so that your application either iterates through multiple results or extracts the first and only document in the cursor. See the Additional Information section of this guide to find a link to the full list of database commands.

The raw command response contains the following fields:

Field
Description
<command result>
Fields specific to the database command. For example, the count command returns the n field.
ok
Whether the command has succeeded (1) or failed (0). The library raises a CommandException if the ok field is 0.
operationTime
The logical time of the operation. MongoDB uses the logical time to order operations. To learn more about this concept, see our blog post about the Global Logical Clock.
$clusterTime
A document that contains the signed cluster time. Cluster time is a logical time used for the ordering of operations.

Command Example

The following example uses the command() method to run the dbStats command to retrieve storage statistics for the accounts database:

$database = $client->accounts;
$command = ['dbStats' => 1];
// dbStats returns a single document
$cursor = $database->command($command);
// Print the first document in the cursor
echo json_encode($cursor->toArray()[0]), PHP_EOL;

The output of this command includes information about the collections in the database and describes the amount and size of data stored across collections:

{"db":"accounts","collections":2,"views":0,"objects":5,"avgObjSize":22,"dataSize":110,
"storageSize":40960,"totalFreeStorageSize":0,"numExtents":0,"indexes":2,"indexSize":40960,
"indexFreeStorageSize":0,"fileSize":0,"nsSizeMB":0,"ok":1}

Additional Information

For more information about the concepts in this guide, see the following documentation in the MongoDB Server manual:

API Documentation

For more information about the command() method, see the following MongoDB PHP Library API documentation:

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