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Read Data from MongoDB

Count Documents

On this page

  • Overview
  • Sample Data
  • Retrieve an Accurate Count
  • Count All Documents
  • Count Specific Documents
  • Customize Count Behavior
  • Retrieve an Estimated Count
  • Customize Estimated Count Behavior
  • API Documentation

Overview

In this guide, you can learn how to use the MongoDB PHP Library to retrieve an accurate and estimated count of the number of documents in a collection. The following methods count documents in a collection:

  • MongoDB\Collection::countDocuments(): Returns the exact number of documents that match a query filter or that exist in a collection

  • MongoDB\Collection::estimatedDocumentCount(): Returns the estimated number of documents in a collection

Sample Data

The examples in this guide use the companies collection in the sample_training database from the Atlas sample datasets. To access this collection from your PHP application, instantiate a MongoDB\Client that connects to an Atlas cluster and assign the following value to your $collection variable:

$collection = $client->sample_training->companies;

To learn how to create a free MongoDB Atlas cluster and load the sample datasets, see the Get Started with Atlas guide.

Retrieve an Accurate Count

Use the MongoDB\Collection::countDocuments() method to count the number of documents in a collection. To count the number of documents that match specific search criteria, pass a query filter to the countDocuments() method.

To learn more about specifying a query, see the Specify a Query guide.

Count All Documents

To return a count of all documents in the collection, pass an empty query filter array to the countDocuments() method, as shown in the following example:

$result = $collection->countDocuments([]);
echo 'Number of documents: ', $result;

Count Specific Documents

To return a count of documents that match specific search criteria, pass a query filter to the countDocuments() method.

The following example counts the number of documents in which the value of the founded_year field is 2010:

$result = $collection->countDocuments(['founded_year' => 2010]);
echo 'Number of companies founded in 2010: ', $result;

Customize Count Behavior

You can modify the behavior of the countDocuments() method by passing an array that specifies option values. The following table describes some options you can set to customize the count operation:

Option
Description
collation
The collation to use for the operation.
Type: array|object
hint
The index to use for the operation.
Type: string|array|object
comment
The comment to attach to the operation.
Type: any valid BSON type
limit
The maximum number of documents to count. This value must be a positive integer.
Type: integer
maxTimeMS
The maximum amount of time in milliseconds that the operation can run.
Type: integer
skip
The number of documents to skip before counting documents.
Type: integer
readPreference
The read preference to use for the operation. To learn more, see Read Preference in the Server manual.
Type: MongoDB\Driver\ReadPreference

The following example uses the countDocuments() method to count the number of documents in which the number_of_employees field has the value 50 and instructs the operation to count a maximum of 100 results:

$result = $collection->countDocuments(
    ['number_of_employees' => 50],
    ['limit' => 100]
);
echo 'Number of companies with 50 employees: ', $result;

Retrieve an Estimated Count

You can retrieve an estimate of the number of documents in a collection by calling the MongoDB\Collection::estimatedDocumentCount() method. The method estimates the amount of documents based on collection metadata, which might be faster than performing an accurate count.

The following example estimates the number of documents in a collection:

$result = $collection->estimatedDocumentCount();
echo 'Estimated number of documents: ', $result;

Customize Estimated Count Behavior

You can modify the behavior of the estimatedDocumentCount() method by passing an array that specifies option values as a parameter. The following table describes the options you can set in the array:

Option
Description
comment
The comment to attach to the operation.
Type: any valid BSON type
maxTimeMS
The maximum amount of time in milliseconds that the operation can run.
Type: integer
readConcern
The read concern to use for the operation. To learn more, see Read Concern in the Server manual.
Type: MongoDB\Driver\ReadConcern
readPreference
The read preference to use for the operation. To learn more, see Read Preference in the Server manual.
Type: MongoDB\Driver\ReadPreference
session
The client session to associate with the operation.
Type: MongoDB\Driver\Session

The following example uses the estimatedDocumentCount() method to return an estimate of the number of documents in the collection and sets a timeout of 1000 milliseconds on the operation:

$result = $collection->estimatedDocumentCount(['maxTimeMS' => 1000]);
echo 'Estimated number of documents: ', $result;

API Documentation

To learn more about any of the methods or types discussed in this guide, see the following API documentation:

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