Multikey Indexes

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)

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

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.