Compound Indexes

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Overview

Sample Data
Create a Compound Index
Additional Information
API Documentation

Overview

Compound indexes hold references to multiple fields within a collection's documents, improving query and sort performance. Use the mongoc_collection_create_indexes_with_opts() function to create compound indexes.

When creating a compound index, you must specify the following components:

The fields to index.
The sort order for each field (ascending or descending). Specify BCON_INT32 (1) for ascending order and BCON_INT32 (-1) for descending order.

Sample Data

The examples in this guide use the movies collection in the sample_mflix database from the Atlas sample datasets. To learn how to create a free MongoDB Atlas cluster and load the sample datasets, see the Get Started with Atlas guide.

Create a Compound Index

The following example creates a compound index on the type and genres fields, with both fields indexed in ascending order:

bson_error_t error;
bson_t *keys = BCON_NEW ("type", BCON_INT32 (1), "genres", BCON_INT32 (1));
mongoc_index_model_t *index_model = mongoc_index_model_new (keys, NULL);
if (mongoc_collection_create_indexes_with_opts (collection, &index_model, 1, NULL, NULL, &error)) {
    printf ("Successfully created index\n");
} else {
    fprintf (stderr, "Failed to create index: %s", error.message);
}
bson_destroy (keys);
mongoc_index_model_destroy (index_model);

The following example performs a query that uses the index created in the preceding code sample:

const bson_t *doc;
bson_t *filter = BCON_NEW ("type", BCON_UTF8 ("movie"),
                           "genres", BCON_UTF8 ("Drama"));
mongoc_cursor_t *results =
    mongoc_collection_find_with_opts (collection, filter, NULL, NULL);
while (mongoc_cursor_next (results, &doc)) {
    char *str = bson_as_canonical_extended_json (doc, NULL);
    printf ("%s\n", str);
    bson_free (str);
}
mongoc_cursor_destroy (results);
bson_destroy (filter);

{ "_id" : ..., "genres" : [ "Crime", "Drama" ], "title" : "Traffic in Souls", "type" : "movie", ... }
{ "_id" : ..., "genres" : [ "Drama" ], "title" : "Laugh, Clown, Laugh", "type" : "movie", ... }
{ "_id" : ..., "genres" : [ "Drama", "Romance" ], "title" : "A Woman of Paris: A Drama of Fate", "type" : "movie", ... }
{ "_id" : ..., "genres" : [ "Drama", "Romance", "Thriller" ], "title" : "He Who Gets Slapped", "type" : "movie", ... }
{ "_id" : ..., "genres" : [ "Drama", "Romance" ], "title" : "Wild Oranges", "type" : "movie", ... }
...

Additional Information

To learn more about compound indexes, see Compound Indexes in the MongoDB Server manual.

To learn about effective indexing strategies using compound indexes, see The ESR Rule in the MongoDB Server manual.

API Documentation

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

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Single Field Indexes

Multikey Indexes