Single Field Indexes

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Overview

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

Overview

Single field indexes are indexes with a reference to a single field of a document in a collection. 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.

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

The field on which to create the index
The sort order for the indexed values as either ascending or 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 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 Single Field Index

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

# Creates an index on the "title" field
collection.indexes.create_one({ title: 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 title in the list, as shown in the following output:

# Lists all indexes on the collection
puts collection.indexes.collect(&:to_json)

{"v": 2, "key": {"title": 1}, "name": "title_1"}

Example Query

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

# Finds a document with the title "Sweethearts" by using the newly created index
filter = { title: 'Sweethearts' }
doc = collection.find(filter).first
if doc
  puts doc.to_json
else
  puts "No document found"
end

{"_id":...,"plot":"A musical comedy duo...",
"genres":["Musical"],...,"title":"Sweethearts",...}

Additional Information

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

To learn more about single field indexes, see Single Field 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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Indexes

Compound