Creates an index on the given field(s), or does nothing if the index already exists

Description

public bool MongoCollection::ensureIndex ( string|array $key|keys [, array $options = array() ] )

This method creates an index on the collection and the specified fields. The key specification can either be just a single field name as string, or an array containing one or more field names with their sort direction.

Parameters

keys

An array of fields by which to sort the index on. Each element in the array has as key the field name, and as value either 1 for ascending sort, or -1 for descending sort.

options

This parameter is an associative array of the form array("optionname" => <boolean>, ...). Currently supported options are:

"unique"

Create a unique index.

Warning
A unique index cannot be created on a field if multiple existing documents do not contain the field. The field is effectively NULL for these documents and thus already non-unique.
"dropDups"

If a unique index is being created and duplicate values exist, drop all but one duplicate value.
"background"

If you are using MongoDB version 1.3.2+, you can create indexes in the background while other operations are taking place. By default, index creation happens synchronously. If you specify TRUE with this option, index creation will be asynchronous.
"safe"

Starting with driver version 1.0.4, you can specify a boolean value for checking if the index creation succeeded. The driver will throw a MongoCursorException if index creation failed.

If you are using replication and the master has changed, using "safe" will make the driver disconnect from the master, throw and exception, and attempt to find a new master on the next operation (your application must decide whether or not to retry the operation on the new master).

If you do not use "safe" with a replica set and the master changes, there will be no way for the driver to know about the change so it will continuously and silently fail to write.
"name"

Starting with driver version 1.0.5 you can specify an index name. This can be useful if you are indexing many keys and Mongo complains about the index name being too long.
"timeout"

Integer, defaults to MongoCursor::$timeout. If "safe" is set, this sets how long (in milliseconds) for the client to wait for a database response. If the database does not respond within the timeout period, a MongoCursorTimeoutException will be thrown.

Return Values

Returns TRUE.

Changelog

Version	Description
1.0.2	Changed "options" parameter from boolean to array. Pre-1.0.2, the second parameter was an optional boolean value specifying a unique index.
1.0.11	"safe" will trigger master failover, if necessary.
1.0.11	MongoException will be thrown if index name (either generated or set) is longer than 128 bytes.
1.2.0	Added timeout option.
1.3.0	The `options` parameter does no longer accept just a boolean to signify a unique index. Instead, this now has to be done with array('unique' => true).

Errors/Exceptions

Throws MongoException if the index name is longer than 128 bytes. (Version 1.0.11+)

Throws MongoCursorException if the "safe" option is set and the index creation fails.

Throws MongoCursorTimeoutException if the "safe" option is set 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.

Examples

Example #1 MongoCollection::ensureIndex() example


<?php

$c = new MongoCollection($db, 'foo');

// create an index on 'x' ascending
$c->ensureIndex('x');

// create an index on 'y' ascending
$c->ensureIndex(array('y' => 1));

// create an index on 'z' ascending and 'zz' descending
$c->ensureIndex(array('z' => 1, 'zz' => -1));

// create a unique index on 'x'
$c->ensureIndex(array('x' => 1), array("unique" => true));

?>

Example #2 Drop duplicates example


<?php

$collection->insert(array("username" => "joeschmoe"));
$collection->insert(array("username" => "joeschmoe"));

/*
 * index creation fails, you can't create a unique index on a key with 
 * non-unique values
 */
$collection->ensureIndex(array("username" => 1), array("unique" => 1));

/*
 * index creation succeeds: one of the documents is removed from the collection
 */
$collection->ensureIndex(array("username" => 1), array("unique" => 1, "dropDups" => 1));

/* 
 * now we have a unique index, more inserts with the same username (such as the
 * one below) will fail
 */
$collection->insert(array("username" => "joeschmoe"));

?>

Example #3 Geospatial Indexing

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


<?php

$collection->ensureIndex(array("loc" => "2d"));

?>

MongoCollection::ensureIndex