Single Field Indexes

Overview

Single field indexes are indexes that hold a reference to a single field in a collection's documents. These indexes improve single field query and sort performance. They also support

TTL Indexes that automatically remove documents from a collection after a certain amount of time or at a specified clock time.

To create a single field index, call the

create_index() method and specify a document containing the following information:

Fields on which to create the index.
Sort order for the indexed values. Use 1 for ascending or -1 for descending.

Note

The default _id_ index is an example of a single field index. This index is automatically created on the _id field when a new collection is created.

Sample Data

The examples in this guide use the movies collection in the sample_mflix database from the Atlas sample datasets. To access this collection from your C++ application, instantiate a mongocxx::client that connects to an Atlas cluster and assign the following values to your db and collection variables:

auto db = client["sample_mflix"];
auto collection = db["movies"];

To learn how to create a free MongoDB Atlas cluster and load the sample datasets, see the Get Started with Atlas guide.

Create Single-Field Index

The following example uses the create_index() method to create an ascending single field index on the title field:

auto index_specification = make_document(kvp("title", 1));
auto result = collection.create_index(index_specification.view());

The following query is covered by the index created in the preceding code example:

auto document = collection.find_one(make_document(kvp("title","Peter Pan")));
std::cout << bsoncxx::to_json(*document) << std::endl;

{ "_id" :..., "plot" : "Peter Pan enters the nursery of the Darling children...",
"genres" : [ "Adventure", "Fantasy", "Family" ], "runtime" : 105,...}

Additional Information

To view runnable examples that demonstrate how to manage indexes, see

Optimize Queries with Indexes.

To learn more about indexes, see the following resources in the MongoDB Server manual:

API Documentation

To learn more about the methods discussed in this guide, see the following API documentation:

Back

Work with Indexes

Compound Indexes