Multikey Indexes

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Overview

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

Overview

Multikey indexes are indexes that improve the performance of queries on array-valued fields. You can create a multikey index on a collection by using the create_one method and the same syntax that you use to create a single field index.

When creating a multikey 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 Multikey Index

Use the create_one method to create a multikey index. The following example creates an index in ascending order on the cast field:

collection.indexes.create_one({ cast: 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 cast in the list, as shown in the following output:

puts collection.indexes.collect(&:to_json)

{"v": 2, "key": {"cast": 1}, "name": "cast_1"}

Example Query

The following is an example of a query that is covered by the index created on the cast field:

filter = { cast: { '$all' => ['Aamir Khan', 'Kajol'] } }
doc = collection.find(filter).first
if doc
  puts doc.to_json
else
  puts "No document found"
end

{"_id":...,"title":"Fanaa",...,"cast": ["Aamir Khan", "Kajol", "Rishi Kapoor", "Tabu"],...}

Additional Information

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

To learn more about multikey indexes, see Multikey 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:

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