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Indexes help resolve queries efficiently. Without indexes, MongoDB must iterate through every document in the collection to find the documents that match the query.

It will waste time and require MongoDB to handle such information. Therefore, in today’s article, we will learn how to create indexes in MongoDB.

Creating Indexes in MongoDB

An index is a specialized data structure that holds a limited subset of a dataset in an accessible format. The values ​​of a specific field or set of fields are stored in the index, sorted by the field values ​​indicated in the index.

MongoDB supports different types of indexes. Single field, composite index, multi-key index, geospatial index, hash index, and clustered index are some of them.

grammar:

db.COLLECTION.createIndex({ KEY_NAME:1 })

1. KEY_NAME is the name of the field to be indexed.
2. The previous point indicates that the order should be ascending. So the index must be constructed with -1 in descending order.
3. The createIndex() method accepts a list of optional parameters. The list is as follows.
   • unique is a boolean variable that creates a unique index, preventing the collection from accepting insertion of documents where the index key or keys already exist. To create a unique index, enter true. The default value is set to false.
   • Boolean variable background Builds the index in the background so it does not interfere with other database operations. To build in the background, specify true. The default value is set to false.
   • If the boolean variable sparse is set to true, the index will only reference documents with the specified fields. Although these indexes take up less space, they may behave differently (especially with sorting). false is the default setting.
   • The string variable name contains the name of the index. If no index name is provided, MongoDB creates one by concatenating the name of the index field and the sort order.
   • The default language for string variables is the language used to build the stop word list and the stemmer and tokenizer standards for the text index.
   • The integer variable expireAfterSeconds defines a time-to-live (TTL) value in seconds that limits how long MongoDB retains documents in this collection.

Let's use the following example to understand the above ideas:

> db.users.createIndex({ "email": 1, "country": -1 })

In the example above, we created a new composite index where email is stored in descending order and country is sorted in ascending order. Every time a query is executed, the index is first sorted by the user's email and then by the country within each email value.