Databases and Collections
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Overview
In this guide, you can learn how to use MongoDB databases and collections with the MongoDB PHP Library.
MongoDB organizes data into a hierarchy of the following levels:
Databases: Top-level data structures in a MongoDB deployment that store collections.
Collections: Groups of MongoDB documents. They are analogous to tables in relational databases.
Documents: Units that store literal data such as string, numbers, dates, and other embedded documents. For more information about document field types and structure, see the Documents guide in the MongoDB Server manual.
Access a Database
Access a database by passing the database name to the MongoDB\Client::selectDatabase()
method.
The following example accesses a database named test_database
:
$db = $client->selectDatabase('test_database');
Alternatively, you can implicitly call the MongoDB\Client::__get()
magic method on
a client object. This method allows you to select a database by using the syntax for
accessing a class property. The following example uses this shorthand syntax to access
the test_database
database:
$db = $client->test_database;
Tip
To learn more about __get()
and PHP magic methods, see the following resources:
MongoDB\Client::__get()
in the library API documentationMagic Methods in the PHP manual
Access a Collection
Access a collection by using either of the following methods:
MongoDB\Client::selectCollection()
: Pass the database and collection names as parametersMongoDB\Database::selectCollection()
: Pass the collection name as a parameter
The following example accesses a collection named test_collection
by using the
MongoDB\Database::selectCollection()
method:
$collection = $client->test_database->selectCollection('test_collection');
Tip
If the provided collection name does not already exist in the database, MongoDB implicitly creates the collection when you first insert data into it.
Alternatively, you can implicitly call the MongoDB\Database::__get()
magic method on
a database object. This method allows you to select a collection by using the syntax for
accessing a class property. The following example uses this shorthand syntax to access
the test_collection
collection:
$collection = $db->test_collection;
To learn more, see the MongoDB\Database::__get()
API documentation.
Create a Collection
Pass a collection name to the MongoDB\Database::createCollection()
method to
explicitly create a collection in a MongoDB database.
The following example creates a collection named example_collection
:
$result = $client->test_database->createCollection('example_collection');
You can specify collection options, such as maximum size and document
validation rules, by passing them as an array to the createCollection()
method.
For a full list of optional parameters, see the API documentation.
Get a List of Collections
You can query for a list of collections in a database by calling the
MongoDB\Database::listCollections()
method. The method returns a
cursor containing all collections in the database and their associated metadata.
The following example calls the listCollections()
method and iterates over
the returned iterator to print the collections from the Access a Collection
and Create a Collection examples:
foreach ($client->test_database->listCollections() as $collectionInfo) { print_r($collectionInfo) . PHP_EOL; }
MongoDB\Model\CollectionInfo Object ( [name] => example_collection [type] => collection ... ) MongoDB\Model\CollectionInfo Object ( [name] => test_collection [type] => collection ... )
Delete a Collection
You can delete a collection from the database by using the MongoDB\Database::dropCollection()
method.
The following example deletes the test_collection
collection:
$client->test_database->dropCollection('test_collection');
Warning
Dropping a Collection Deletes All Data in the Collection
Dropping a collection from your database permanently deletes all documents and all indexes within that collection.
Drop a collection only if you no longer need the data in it.
Configure Read and Write Operations
You can control how read and write operations run on replica sets by specifying a read preference, read concern, or write concern.
By default, databases inherit read and write settings from the MongoDB\Client
instance. Collections inherit these settings from the MongoDB\Client
or
MongoDB\Database
instance on which the selectCollection()
method is called.
You can change these settings by passing an options array to the
MongoDB\Client::selectDatabase()
, MongoDB\Client::selectCollection()
, or
MongoDB\Database::selectCollection()
methods.
To learn more about setting a read preference, read concern, and write concern, see the Specify How CRUD Operations Run on Replica Sets guide.
API Documentation
To learn more about any of the methods or types discussed in this guide, see the following API documentation: