1. Introduction

In this tutorial, we will delve into one of the key aspects of GraphQL - mutations. Mutations are defined as the operations that are used to create, update, or delete data in GraphQL. Our focus will be on the best practices to ensure that your mutations are efficient, secure, and easy to maintain.

By the end of this tutorial, you will learn:
- The basics of mutations in GraphQL
- How to write efficient and secure mutations
- Best practices for handling mutations

To make the most out of this tutorial, you should have a basic understanding of GraphQL and JavaScript.

2. Step-by-Step Guide

Mutations in GraphQL

In GraphQL, mutations are the methods you use to change data on the server, such as adding a new record or updating an existing one.

One of the important things to remember is that unlike queries, mutations always need to be executed in the order they are received. This is crucial because mutations can change the state of your data on the server.

Best Practices for Writing Mutations

1. Make mutations specific: It's better to have specific mutations for specific purposes. For example, instead of having one mutation updateUser, it's more efficient to have updateUserName, updateUserEmail, etc.

2. Always return the object after mutation: It's a best practice to return the object after mutation. This allows the client to get the updated data right after the mutation, saving an extra query.

3. Input validation: Always validate the input data before performing a mutation. This can help prevent unwanted data from entering your database.

4. Error handling: Be sure to handle errors properly. If a mutation fails, it should provide a clear error message to the client.

3. Code Examples

Let's look at some examples of how to write mutations following these best practices.

Example 1: A specific mutation to update a user's email.

mutation UpdateUserEmail($email: String!, $id: ID!) {
  updateUserEmail(email: $email, id: $id) {
    id
    email
  }
}

In this example, the mutation updateUserEmail takes two arguments, email and id. After updating the user's email, it returns the updated user's id and email.

Example 2: Input validation before performing mutation.

mutation AddNewUser($user: UserInput!) {
  addUser(user: $user) @validate {
    id
    name
    email
  }
}

Here, the @validate directive is used to validate the input before performing the mutation. If the input is not valid, the mutation will not be executed.

4. Summary

In this tutorial, we have covered the basics of mutations in GraphQL and some best practices for writing mutations. We learned that it's important to make mutations specific, always return the object after mutation, validate the input, and handle errors properly.

Next, you can delve deeper into GraphQL by learning about subscriptions, which allow you to push updates to your clients in real-time.

5. Practice Exercises

1. Write a mutation to delete a user by id. Remember to return the deleted user's id.

2. Write a mutation to update a user's name and email. Validate the input before performing the mutation.

3. Assume you have a blog application. Write a mutation to add a new post. The post should have a title, content, and author's id.

Remember to practice regularly and apply the best practices you've learned in this tutorial. Happy coding!