OPTIONS

db.collection.ensureIndex()

Definition

db.collection.ensureIndex(keys, options)

Creates an index on the specified field if the index does not already exist.

The ensureIndex() method has the following fields:

Parameter Type Description
keys document

A document that contains the field and value pairs where the field is the index key and the value describes the type of index for that field. For an ascending index on a field, specify a value of 1; for descending index, specify a value of -1.

MongoDB supports several different index types including text, geospatial, and hashed indexes. See Index Type Documentation for more information.

options document Optional. A document that contains a set of options that controls the creation of the index. See Options for details.

Options

The options document contains a set of options that controls the creation of the index. Different index types can have additional options specific for that type.

Options for All Index Types

The following options are available for all index types unless otherwise specified:

Parameter Type Description
background Boolean Optional. 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.
unique Boolean

Optional. Creates a unique index so that the collection will not accept insertion of documents where the index key or keys match an existing value in the index. Specify true to create a unique index. The default value is false.

The option is unavailable for hashed indexes.

name string

Optional. The name of the index. If unspecified, MongoDB generates an index name by concatenating the names of the indexed fields and the sort order.

Whether user specified or MongoDB generated, index names including their full namespace (i.e. database.collection) cannot be longer than the Index Name Limit.

dropDups Boolean

Optional. Creates a unique index on a field that may have duplicates. MongoDB indexes only the first occurrence of a key and removes all documents from the collection that contain subsequent occurrences of that key. Specify true to create unique index. The default value is false.

The option is unavailable for hashed indexes.

Deprecated since version 2.6.

Warning

dropDups will delete data from your collection when building the index.

sparse Boolean

Optional. If true, the index only references documents with the specified field. These indexes use less space but behave differently in some situations (particularly sorts). The default value is false. See Sparse Indexes for more information.

Changed in version 2.6: 2dsphere indexes are sparse by default and ignore this option. For a compound index that includes 2dsphere index key(s) along with keys of other types, only the 2dsphere index fields determine whether the index references a document.

2d, geoHaystack, and text indexes behave similarly to the 2dsphere indexes.

expireAfterSeconds integer Optional. Specifies a value, in seconds, as a TTL to control how long MongoDB retains documents in this collection. See Expire Data from Collections by Setting TTL for more information on this functionality. This applies only to TTL indexes.
v index version Optional. The index version number. The default index version depends on the version of mongod running when creating the index. Before version 2.0, the this value was 0; versions 2.0 and later use version 1, which provides a smaller and faster index format. Specify a different index version only in unusual situations.

Options for text Indexes

The following options are available for text indexes only:

Parameter Type Description
weights document Optional. For text indexes, a document that contains field and weight pairs. The weight is an integer ranging from 1 to 99,999 and denotes the significance of the field relative to the other indexed fields in terms of the score. You can specify weights for some or all the indexed fields. See Control Search Results with Weights to adjust the scores. The default value is 1.
default_language string Optional. For text indexes, the language that determines the list of stop words and the rules for the stemmer and tokenizer. See Text Search Languages for the available languages and Specify a Language for Text Index for more information and examples. The default value is english.
language_override string Optional. For text indexes, the name of the field, in the collection’s documents, that contains the override language for the document. The default value is language. See Use any Field to Specify the Language for a Document for an example.
textIndexVersion integer

Optional. For text indexes, the text index version number. Version can be either 1 or 2.

In MongoDB 2.6, the default version is 2. MongoDB 2.4 can only support version 1.

New in version 2.6.

Options for 2dsphere Indexes

The following option is available for 2dsphere indexes only:

Parameter Type Description
2dsphereIndexVersion integer

Optional. For 2dsphere indexes, the 2dsphere index version number. Version can be either 1 or 2.

In MongoDB 2.6, the default version is 2. MongoDB 2.4 can only support version 1.

New in version 2.6.

Options for 2d Indexes

The following options are available for 2d indexes only:

Parameter Type Description
bits integer

Optional. For 2d indexes, the number of precision of the stored geohash value of the location data.

The bits value ranges from 1 to 32 inclusive. The default value is 26.

min number Optional. For 2d indexes, the lower inclusive boundary for the longitude and latitude values. The default value is -180.0.
max number Optional. For 2d indexes, the upper inclusive boundary for the longitude and latitude values. The default value is 180.0.

Options for geoHaystack Indexes

The following option is available for geoHaystack indexes only:

Parameter Type Description
bucketSize number

For geoHaystack indexes, specify the number of units within which to group the location values; i.e. group in the same bucket those location values that are within the specified number of units to each other.

The value must be greater than 0.

Behaviors

The ensureIndex() method has the behaviors described here.

  • To add or change index options you must drop the index using the dropIndex() method and issue another ensureIndex() operation with the new options.

    If you create an index with one set of options, and then issue the ensureIndex() method with the same index fields and different options without first dropping the index, ensureIndex() will not rebuild the existing index with the new options.

  • If you call multiple ensureIndex() methods with the same index specification at the same time, only the first operation will succeed, all other operations will have no effect.

  • Non-background indexing operations will block all other operations on a database.

  • MongoDB will not create an index on a collection if the index entry for an existing document exceeds the Maximum Index Key Length. Previous versions of MongoDB would create the index but not index such documents.

    Changed in version 2.6.

Examples

Create an Ascending Index on a Single Field

The following example creates an ascending index on the field orderDate.

db.collection.ensureIndex( { orderDate: 1 } )

If the keys document specifies more than one field, then ensureIndex() creates a compound index.

Create an Index on a Multiple Fields

The following example creates a compound index on the orderDate field (in ascending order) and the zipcode field (in descending order.)

db.collection.ensureIndex( { orderDate: 1, zipcode: -1 } )

A compound index cannot include a hashed index component.

Note

The order of an index is important for supporting sort() operations using the index.

See also