Optimize Queries With Indexes

Declare and Create an Index

When using Mongoid, you can declare your index using the index macro and then create it using the create_indexes command.

The following code example shows how to declare and create an ascending index named cuisine_index on the cuisine field in the Restaurant class:

class Restaurant
 include Mongoid::Document
 
 field :name, type: String
 field :cuisine, type: String
 field :borough, type: String
 index({ cuisine: 1}, { name: "cuisine_index", unique: false })
end
 
Restaurant.create_indexes

The index macro defines the index you want to create and the create_indexes command creates it in the restaurants collection.

When defining an index, the first hash object contains the field you want to index and its direction. 1 represents an ascending index, and -1 represents a descending index. The second hash object contains index options. To learn more about index options, see the API Documentation section.

class Restaurant
 include Mongoid::Document
 field :borough, as: :b
 index({ b: 1}, { name: "borough_index" })
end

Create an Index on Embedded Document Fields

You can define an index on embedded document fields. The following code example shows how to declare an ascending index on the street field, which is embedded within the address field in the Restaurant model.

class Address
 include Mongoid::Document
 field :street, type: String
end
class Restaurant
 include Mongoid::Document
 embeds_many :addresses
 index({"addresses.street": 1})
end

Create a Compound Index

You can define a compound index on multiple fields. The following code example shows how to declare a compound index that is ascending on the borough field and descending on the name field.

class Restaurant
 include Mongoid::Document
 field :name, type: String
 field :borough, type: String
 index({borough: 1, name: -1}, { name: "compound_index"})
end

Create a Geospatial Index

You can define a 2dsphere index on fields that contain GeoJSON objects or coordinate pairs. The following example defines a 2dsphere index on a field that contains GeoJSON objects:

class Restaurant
 include Mongoid::Document
 field :location, type: Array
 index({location: "2dsphere"}, { name: "location_index"})
end

For more information on 2dsphere indexes, see the 2dsphere guide in the MongoDB Server manual.

For more information on the GeoJSON type, see the GeoJSON Objects guide in the MongoDB Server manual.

Create a Sparse Index

You can define a sparse index on fields that are not present in all documents. The following code example defines a sparse index on the borough field:

class Restaurant
 include Mongoid::Document
 
 field :name, type: String
 field :cuisine, type: String
 field :borough, type: String
 index({ borough: 1}, { sparse: true })
end

For more information on sparse indexes, see the Sparse Indexes guide in the MongoDB Server manual.

Create Multiple Indexes

You can define multiple indexes within your model and create them using a single create_indexes call. The following example shows how to create multiple indexes at the same time:

class Restaurant
 include Mongoid::Document
 
 field :name, type: String
 field :cuisine, type: String
 field :borough, type: String
 
 index({ name: 1})
 index({ cuisine: -1})
end
Restaurant.create_indexes

Drop Indexes

You can drop all indexes in your collection. The following example drops all indexes in the Restaurant model:

Restaurant.remove_indexes

Atlas Search Indexes

You can declare and manage Atlas Search indexes using Mongoid.

To declare a search index, use the search_index macro within your model. To create the search indexes declared within a model, use the create_search_indexes command. The following code example shows how to declare and create an Atlas Search index named my_search_index. The index is on the name and cuisine fields and is dynamic.

class Restaurant
 include Mongoid::Document
 
 field :name, type: String
 field :cuisine, type: String
 field :borough, type: String
 search_index :my_search_index, 
 mappings: { 
 fields: { 
 name: { 
 type: "string" 
 },
 cuisine: {
 type: "string"
 }
 }, 
 dynamic: true 
 }
end
Restaurant.create_search_indexes

To learn more about the syntax for creating an Atlas Search index, see the Create an Atlas Search Index guide in the MongoDB Atlas documentation.

Restaurant.remove_search_indexes

Restaurant.search_indexes.each { |index| puts index }