================================
MongoDBCollection::createIndex()
================================

.. default-domain:: mongodb

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   :class: singlecol
                    
Definition
----------

.. phpmethod:: MongoDB\\Collection::createIndex($key, $options)
               
   Create an index for the collection.
   
   .. code-block:: php
                   
      function createIndex($key, array $options = []): string

   ``createIndex()`` accepts the following parameters:
   
   .. include:: /includes/apiargs/MongoDBCollection-method-createIndex-param.rst

   The ``$options`` parameter accepts all index options that your
   MongoDB version supports. MongoDB 3.2 includes the following options:
                
   .. include:: /includes/apiargs/MongoDBCollection-method-createIndex-option.rst

   For a full list of the supported index creation options, refer to
   the :manual:`createIndexes </reference/command/createIndexes>`
   command reference in the MongoDB manual.

Output
------

Returns the name of the created index as a string.
                
Examples
--------

Create a Compound Index
~~~~~~~~~~~~~~~~~~~~~~~

The following operation creates a :manual:`compound index
</core/index-compound>` on the ``borough`` and ``cuisine`` fields
in the ``restaurants`` collection.

.. code-block:: php
                
   <?php
   
   $database = new MongoDB\Client;

   $collection = $database->selectCollection('example','restaurants');

   $keys = ['borough' => 1, 'cuisine' => 1];

   $indexString = $collection->createIndex($keys, ['name' => 'compound']);

   var_dump($indexString);

The output would resemble the following:

.. code-block:: none
                
   string(8) "compound"

Create a Partial Index
~~~~~~~~~~~~~~~~~~~~~~

The following operation adds a :manual:`partial index
</core/index-parital>` on the ``borough`` field in the ``restaurants``
collection in the ``example`` database. The partial index indexes only
fields where the ``borough`` field exists.

.. code-block:: php
                
   <?php
   
   $database = new MongoDB\Client;

   $collection = $database->selectCollection('example','restaurants');

   $indexString = $collection->createIndex(
      ['borough' => 1], 
      ['partialFilterExpression'=>
         ['borough'=>
            ['$exists'=>true]
   ]]);
   
   var_dump($indexString);

The output would resemble::
                
   string(9) "borough_1"

.. seealso::
   
   - :phpmethod:`MongoDB\\Collection::createIndexes`
   - :doc:`/tutorial/indexes`
   - :manual:`createIndexes </reference/command/createIndexes>` 
     command reference in the MongoDB manual
   - :manual:`Index documentation </indexes>`