ensureIndex() - Creates a new index

indexSpec

This argument specifies a field in the document on which the index is to be created. It might include a data type definition

indexName

This argument specifies a name for an index. A name is generated if it is not specified.

expireAfterSeconds

Optional. Specifies a value, in seconds, at which point the documents in this collection are deleted

expireAt

Optional.

unique (true | false)

This optional argument specifies whether the index is unique.

indexOptions

This optional argument can have one of the following options:

name

This argument specifies a name of an index. A name is generated if not specified.

array (true | false)

This argument specifies an array of elements.

unique (true | false)

This argument specifies whether the index is unique.

Example 1: Create an index on field 'author' in ascending order, by using the default type string with default length 50.

db.books.ensureIndex({"author": 1})

Sample output:

Index <books_xauthor> was created successfully.

Example 2: Create an index on field 'category' with type string and field length 40.

db.books.ensureIndex({"category": [1, "$string", 40]})

Sample output:

Index <books_xcategory> was created successfully.

Example 3: Create an index on field price with type number in descending order, name it mypriceidx.

db.books.ensureIndex({"price": [-1, "$number"]}, “mypriceidx”)

Sample output:

Index <mypriceidx> was created successfully.