1. Introduction

1.1. Brief explanation of the tutorial's goal

This tutorial aims to give you an understanding of how to use compound and multikey indexes in MongoDB. By mastering these types of indexes, you'll be able to create more efficient queries and boost your application's performance.

1.2. What the user will learn

By the end of this tutorial, you will understand:
- What compound and multikey indexes are.
- How to create and use them effectively.
- The best practices for using these indexes.

1.3. Prerequisites

• Basic knowledge of MongoDB.
• MongoDB installed on your machine.
• Basic understanding of how indexes work in databases.

2. Step-by-Step Guide

2.1. Understanding Compound Indexes

In MongoDB, compound indexes are a way to create a single index on multiple fields. A compound index can support queries that match on multiple fields.

db.collection.createIndex( { field1: 1, field2: -1 } )

In the above example, we are creating a compound index on field1 in ascending order and field2 in descending order.

2.2. Understanding Multikey Indexes

Multikey indexes are used to index the content stored in arrays. If you index a field that holds an array value, MongoDB creates separate index entries for every element of the array.

db.collection.createIndex( { field1: 1, "field2.field3": 1 } )

In the above example, we are creating a multikey index on field2.field3. If field3 is an array, MongoDB would index each value of the array.

3. Code Examples

3.1. Example 1: Creating a Compound Index

db.products.createIndex( { category: 1, price: -1 } )

This creates a compound index where category is in ascending order and price is in descending order.

3.2. Example 2: Creating a Multikey Index

db.students.createIndex( { "grades.score": 1 } )

This creates a multikey index on the score field of the grades array.

4. Summary

• Compound indexes allow us to create a single index on multiple fields.
• Multikey indexes are used to index the content stored in arrays.
• The order of fields in compound index matters.
• MongoDB automatically determines whether to create a multikey index if the indexed field is an array.

5. Practice Exercises

5.1. Exercise 1

Create a compound index on the products collection for the fields category and name, both in ascending order.

Solution

db.products.createIndex( { category: 1, name: 1 } )

5.2. Exercise 2

Create a multikey index on the students collection for the scores field in the grades array.

Solution

db.students.createIndex( { "grades.scores": 1 } )

Remember to keep practicing and experimenting with different types of indexes and field orders to understand the performance implications. Happy coding!