Compound Indexes

On this page

Overview

Sample Data
Create a Compound Index
Verify Index Creation
Example Query
Additional Information
API Documentation

Overview

Compound indexes hold references to multiple fields within a collection's documents, improving query and sort performance.

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

The fields on which to create the index
The sort order for each field (ascending or descending)

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 Ruby application, create a Mongo::Client object that connects to an Atlas cluster and assign the following values to your database and collection variables:

database = client.use('sample_mflix')
collection = database[:movies]

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

Use the create_one method to create a compound index. The following example creates an index in descending order on the runtime field and in ascending order on the year field:

collection.indexes.create_one({ runtime: -1, year: 1 })

Verify Index Creation

You can verify that the index was created by listing the indexes in the collection. You should see an index for runtime and year in the list, as shown in the following output:

puts collection.indexes.collect(&:to_json)

{"v": 2, "key": {"runtime": -1, "year": 1}, "name": "runtime_-1_year_1"}

Example Query

The following is an example of a query that is covered by the index created on the runtime and year fields:

filter = { '$and' => [
    { runtime: { '$gt' => 90 } },
    { year: { '$gt' => 2005 } }
  ] }
doc = collection.find(filter).first
if doc
  puts doc.to_json
else
  puts "No document found"
end

{"_id":...,"runtime": 91,...,"title": "Monster House",...,"year": 2006,...}

Additional Information

To view runnable examples that demonstrate how to manage indexes, see Optimize Queries by Using Indexes.

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

API Documentation

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

Back

Single Field

Multikey