Create Indexes

Indexes support the efficient execution of queries in MongoDB. To create an index on a field or fields, pass an index specification document to the MongoCollection.createIndex() method.

The MongoDB Scala Driver provides the Indexes class that includes helper methods to create index specification documents for the various MongoDB Index key types.

Note

MongoDB only creates an index if an index of the same specification does not already exist.

Prerequisites

  • Include the following import statements:

     import org.mongodb.scala._

 import org.mongodb.Indexes
 import org.mongodb.IndexOptions
 import org.mongodb.Filters
important

This guide uses the Observable implicits as covered in the Quick Start Primer.

Connect to a MongoDB Deployment

Connect to a MongoDB deployment and declare and define a MongoDatabase and a MongoCollection instances.

For example, include the following code to connect to a standalone MongoDB deployment running on localhost on port 27017 and define database to refer to the test database and collection to refer to the restaurants collection:

val mongoClient: MongoClient = MongoClient()
val database: MongoDatabase = mongoClient.getDatabase("test")
val collection: MongoCollection[Document] = database.getCollection("restaurants")

For additional information on connecting to MongoDB, see Connect to MongoDB.

Ascending Index

To create a specification for an ascending index, use the Indexes.ascending helper methods.

Single Ascending Index

The following example creates an ascending index on the name field:

collection.createIndex(Indexes.ascending("name"))
          .printResults()

Compound Ascending Index

The following example creates an ascending compound index on the stars field and the name field:

collection.createIndex(Indexes.ascending("stars", "name"))
          .printResults()

For an alternative way to create a compound index, see Compound Indexes.

Descending Index

To create a specification of a descending index, use the Indexes.descending helper methods.

Single Descending Key Index

The following example creates a descending index on the stars field:

collection.createIndex(Indexes.descending("stars"))
          .printResults()

Compound Descending Key Index

The following example creates a descending compound index on the stars field and the name field:

collection.createIndex(Indexes.descending("stars", "name"))
          .printResults()

For an alternative way to create a compound index, see Compound Indexes.

Compound Indexes

To create a specification for a compound index, use the Indexes.compoundIndex helper methods.

Note

To create a specification for a compound index where all the keys are ascending, you can use the ascending() method. To create a specification for a compound index where all the keys are descending, you can use the descending() method.

The following example creates a compound index with the stars field in descending order and the name field in ascending order:

collection.createIndex(
              Indexes.compoundIndex(Indexes.descending("stars"), 
                                    Indexes.ascending("name")))
          .printResults()

Text Indexes

MongoDB provides text indexes to support text search of string content. Text indexes can include any field whose value is a string or an array of string elements. To create a specification for a text index, use the Indexes.text helper method.

The following example creates a text index on the name field:

collection.createIndex(Indexes.text("name"))
          .printResults()

Hashed Index

To create a specification for a hashed index index, use the Indexes.hashed helper method.

The following example creates a hashed index on the _id field:

collection.createIndex(Indexes.hashed("_id"))
          .printResults()

Geospatial Indexes

To support geospatial queries, MongoDB supports various geospatial indexes.

2dsphere

To create a specification for a 2dsphere index, use the Indexes.geo2dsphere static helper methods.

The following example creates a 2dsphere index on the "contact.location" field:

collection.createIndex(Indexes.geo2dsphere("contact.location"))
          .printResults()

IndexOptions

import org.mongodb.scala.model.IndexOptions

In addition to the index specification document, the createIndex() method can take an index options document, such as to create unique indexes or partial indexes.

The Scala driver provides the IndexOptions class to specify various index options.

Unique Index

The following specifies a unique(true) option to create a unique index on the name and stars fields:

val indexOptions = IndexOptions().unique(true)
collection.createIndex(Indexes.ascending("name", "stars"), indexOptions)
          .printResults()

For more information on unique indexes, see Unique Indexes.

Partial Index

To create a partial index, include a partialFilterExpression as an index option.

The following example creates a partial index on documents that have status field equal to "A".

val partialFilterIndexOptions = IndexOptions()
             .partialFilterExpression(Filters.exists("contact.email"))
collection.createIndex(
                Indexes.descending("name", "stars"), partialFilterIndexOptions)
          .printResults()

For more information on partial indexes, see Partial Indexes.

Get a List of Indexes on a Collection

Use the listIndexes() method to get a list of indexes. The following lists the indexes on the collection:

collection.listIndexes().printResults()

For other index options, see MongoDB Manual.

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