Retrieve Distinct Field Values
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Overview
In this guide, you can learn how to use the MongoDB PHP Library to retrieve the distinct values of a specified field across a collection.
Within a collection, different documents might contain different values for a
single field. For example, one document in a restaurants collection has a
borough value of 'Manhattan', and another has a borough value of
'Queens'. By using the MongoDB PHP Library, you can retrieve all the unique values
that a field contains across multiple documents in a collection.
Sample Data
The examples in this guide use the restaurants collection in the sample_restaurants
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_restaurants->restaurants;
To learn how to create a free MongoDB Atlas cluster and load the sample datasets, see the Get Started with Atlas guide.
MongoDB\Collection::distinct() Method
To retrieve the distinct values for a specified field, call the MongoDB\Collection::distinct()
method and pass in the name of the field you want to find distinct values for.
Retrieve Distinct Values Across a Collection
The following example retrieves the distinct values of the borough field in
the restaurants collection:
$results = $collection->distinct('borough', []); foreach ($results as $value) { echo json_encode($value), PHP_EOL; }
"Bronx" "Manhattan" "Missing" "Queens" "Staten Island"
The operation returns an array that stores each distinct borough field value. Although
several documents have the same value in the borough field, each value appears in the
results only once.
Retrieve Distinct Values Across Specified Documents
You can provide a query filter to the distinct() method to find the distinct
field values across a subset of documents in a collection. A query filter is an expression
that specifies search criteria used to match documents in an operation. For more information
about creating a query filter, see the Specify a Query guide.
The following example retrieves the distinct values of the borough field for
all documents that have a cuisine field value of 'Italian':
$results = $collection->distinct('borough', ['cuisine' => 'Italian']); foreach ($results as $value) { echo json_encode($value), PHP_EOL; }
"Bronx" "Manhattan" "Queens" "Staten Island"
Modify Distinct Behavior
You can modify the behavior of the distinct() method by passing an
array that specifies option values. The following table describes some
options you can set to customize the operation:
Option | Description |
|---|---|
collation | The collation to use for the operation. Type: array|object |
maxTimeMS | The maximum amount of time in milliseconds that the operation can run. Type: integer |
comment | The comment to attach to the operation. Type: any valid BSON type |
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 retrieves the distinct values of the name field for
all documents that have a borough field value of 'Bronx' and a
cuisine field value of 'Pizza'. It also specifies the comment field
in an options array to add a comment to the operation:
$query = ['borough' => 'Bronx', 'cuisine' => 'Pizza']; $options = ['comment' => 'Bronx pizza restaurants']; $results = $collection->distinct('name', $query, $options); foreach ($results as $value) { echo json_encode($value), PHP_EOL; }
"$1.25 Pizza" "18 East Gunhill Pizza" "2 Bros" "Aenos Pizza" "Alitalia Pizza Restaurant" "Amici Pizza And Pasta" "Angie'S Cafe Pizza" ...
API Documentation
To learn more about the distinct() method, see
MongoDB\Collection::distinct() in the API documentation.