# MongoCollection::createIndex

(PECL mongo >=1.5.0)

MongoCollection::createIndex — Creates an index on the specified field(s) if it does not already exist

### Description

public MongoCollection::createIndex ( array `$keys` [, array `$options` = array() ] ) : bool

Creates an index on the specified field(s) if it does not already exist. Fields may be indexed with a direction (e.g. ascending or descending) or a special type (e.g. text, geospatial, hashed).

> Note:

> This method will use the » createIndexes database command when communicating with MongoDB 2.6+. For previous database versions, the method will perform an insert operation on the special `system.indexes` collection.

### Parameters

`keys`

  An array specifying the index's fields as its keys. For each field, the value is either the index direction or » index type. If specifying direction, specify `1` for ascending or `-1` for descending.

`options`

  An array of options for the index creation. We pass all given options straight to the server, but a non-exhaustive list of currently available options include:

  - `"unique"`

    Specify `TRUE` to create a unique index. The default value is `FALSE`. This option applies only to ascending/descending indexes.

    > Note:

    > When MongoDB indexes a field, if a document does not have a value for the field, a `NULL` value is indexed. If multiple documents do not contain a field, a unique index will reject all but the first of those documents. The `"sparse"` option may be used to overcome this, since it will prevent documents without the field from being indexed.

  - `"sparse"`

    Specify `TRUE` to create a sparse index, which only indexes documents containing a specified field. The default value is `FALSE`.

  - `"expireAfterSeconds"`

    The value of this option should specify the number of seconds after which a document should be considered expired and automatically removed from the collection. This option is only compatible with single-field indexes where the field will contain MongoDate values.

    > Note:

    > This feature is available in MongoDB 2.2+. See » Expire Data from Collections by Setting TTL for more information.

  - `"name"`

    A optional name that uniquely identifies the index.

    > Note:

    > By default, the driver will generate an index name based on the index's field(s) and ordering or type. For example, a compound index `array("x" => 1, "y" => -1)` would be named `"x_1_y_-1"` and a geospatial index `array("loc" => "2dsphere")` would be named `"loc_2dsphere"`. For indexes with many fields, it is possible that the generated name might exceed MongoDB's » limit for index names. The `"name"` option may be used in that case to supply a shorter name.

  - `"background"`

    Builds the index in the background so that building an index does not block other database activities. Specify `TRUE` to build in the background. The default value is `FALSE`.

    Warning

    Prior to MongoDB 2.6.0, index builds on secondaries were executed as foreground operations, irrespective of this option. See » Building Indexes with Replica Sets for more information.

  - `"socketTimeoutMS"`

    This option specifies the time limit, in milliseconds, for socket communication. If the server does not respond within the timeout period, a MongoCursorTimeoutException will be thrown and there will be no way to determine if the server actually handled the write or not. A value of `-1` may be specified to block indefinitely. The default value for MongoClient is `30000` (30 seconds).

  The following option may be used with MongoDB 2.6+:

  - `"maxTimeMS"`

    Specifies a cumulative time limit in milliseconds for processing the operation on the server (does not include idle time). If the operation is not completed by the server within the timeout period, a MongoExecutionTimeoutException will be thrown.

  The following options may be used with MongoDB versions before 2.8:

  - `"dropDups"`

    Specify `TRUE` to force creation of a unique index where the collection may contain duplicate values for a key. MongoDB will index the first occurrence of a key and delete all subsequent documents from the collection that contain a duplicate value for that key. The default value is `FALSE`.

    Warning

    `"dropDups"` may delete data from your database. Use with extreme caution.

    > Note:

    > This option is not supported on MongoDB 2.8+. Index creation will fail if the collection contains duplicate values.

  The following options may be used with MongoDB versions before 2.6:

  - `"w"`

    See Write Concerns. The default value for MongoClient is `1`.

  - `"wTimeoutMS"`

    This option specifies the time limit, in milliseconds, for write concern acknowledgement. It is only applicable when `"w"` is greater than `1`, as the timeout pertains to replication. If the write concern is not satisfied within the time limit, a MongoCursorException will be thrown. A value of `0` may be specified to block indefinitely. The default value for MongoClient is `10000` (ten seconds).

  The following options are deprecated and should no longer be used:

  - `"safe"`

    Deprecated. Please use the write concern `"w"` option.

  - `"timeout"`

    Deprecated alias for `"socketTimeoutMS"`.

  - `"wtimeout"`

    Deprecated alias for `"wTimeoutMS"`.

### Return Values

Returns an array containing the status of the index creation. The array contains whether the operation succeeded (`"ok"`), the number of indexes before and after the operation (`"numIndexesBefore"` and `"numIndexesAfter"`), and whether the collection that the index belongs to has been created (`"createdCollectionAutomatically"`). If the index already existed and did not need to be created, a `"note"` field may be present in lieu of `"numIndexesAfter"`.

With MongoDB 2.4 and earlier, a status document is only returned if the write concern is at least `1`. Otherwise, `TRUE` is returned. The fields in the status document are different, except for the `"ok"` field, which signals whether the index creation was successful. Additional fields are described in the documentation for MongoCollection::insert().

### Errors/Exceptions

Throws MongoException if the index name is longer than 128 bytes, or if the index specification is not an array.

Throws MongoDuplicateKeyException if the server could not create the unique index due to conflicting documents.

Throws MongoResultException if the server could not create the index due to an error.

Throws MongoCursorException if the `"w"` option is set and the write fails.

Throws MongoCursorTimeoutException if the `"w"` option is set to a value greater than one and the operation takes longer than MongoCursor::$timeout milliseconds to complete. This does not kill the operation on the server, it is a client-side timeout. The operation in MongoCollection::$wtimeout is milliseconds.

### Examples

Example #1 MongoCollection::createIndex() example

`<?php
$c = new MongoCollection($db, 'foo');
// create an index on 'x' ascending
$c->createIndex(array('x' => 1));
// create a unique index on 'y'
$c->createIndex(array('y' => 1), array('unique' => true));
// create a compound index on 'za' ascending and 'zb' descending
$c->createIndex(array('za' => 1, 'zb' => -1));
?>`

Example #2 Geospatial Indexing

Mongo supports geospatial indexes, which allow you to search for documents near a given location or within a shape. The following example creates a geospatial index on the `"loc"` field:

`<?php
$collection->createIndex(array('loc' => '2dsphere'));
?>`

Example #3 Drop duplicates example

`<?php
$collection->insert(array('username' => 'joeschmoe'));
$collection->insert(array('username' => 'joeschmoe'));
/* Index creation fails, since you cannot create a unique index on a field when
* duplicates exist.
*/
$collection->createIndex(array('username' => 1), array('unique' => 1));
/* MongoDB will one of the conflicting documents and allow the unique index to
* be created.
*/
$collection->createIndex(array('username' => 1), array('unique' => 1, 'dropDups' => 1));
/* We now have a unique index and subsequent inserts with the same username will
* fail.
*/
$collection->insert(array('username' => 'joeschmoe'));
?>`

### See Also

- MongoCollection::deleteIndex() - Deletes an index from this collection
- MongoCollection::deleteIndexes() - Delete all indices for this collection
- The MongoDB » index and » index type documentation.