Create mutation pattern in GraphQL

Introduction

A create mutation lets you add new data to your database. It helps you save new information easily.

When a user signs up and you want to save their details.

When adding a new product to an online store.

When submitting a new comment on a blog post.

When recording a new order in a sales system.

Syntax

GraphQL

mutation CreateItem($input: ItemInput!) {
  createItem(input: $input) {
    id
    name
    description
  }
}

The mutation keyword starts the operation to change data.

$input is a variable holding the new data you want to add.

Examples

This mutation adds a new user with username and email.

GraphQL

mutation CreateUser($input: UserInput!) {
  createUser(input: $input) {
    id
    username
    email
  }
}

This mutation adds a new product with title and price.

GraphQL

mutation AddProduct($input: ProductInput!) {
  addProduct(input: $input) {
    id
    title
    price
  }
}

Sample Program

This mutation adds a new book with its title and author.

GraphQL

mutation CreateBook($input: BookInput!) {
  createBook(input: $input) {
    id
    title
    author
  }
}

# Variables:
# {
#   "input": {
#     "title": "The Great Gatsby",
#     "author": "F. Scott Fitzgerald"
#   }
# }

Important Notes

Always define the input type to specify what data is needed.

Use variables to keep your mutation flexible and reusable.

The server returns the new item's fields you ask for after creation.

Summary

Create mutations add new data to your database.

Use mutation keyword with input variables.

Request the fields you want back after creating the item.

Practice

1. What is the main purpose of a mutation in GraphQL?

easy

A. To optimize query performance

B. To create, update, or delete data in the database

C. To define the schema types

D. To fetch data without changing it

Solution

1. Step 1: Understand GraphQL operation types

   GraphQL has queries for reading data and mutations for changing data.

2. Step 2: Identify mutation role

   Mutations are used to create, update, or delete data in the database.

3. Final Answer:

   To create, update, or delete data in the database -> Option B

4. Quick Check:

   Mutation = change data [OK]

Hint: Mutations always change data, queries only read data [OK]

Common Mistakes:

• Confusing mutations with queries
• Thinking mutations only fetch data
• Mixing schema definition with data operations

2. Which of the following is the correct syntax to start a mutation with an input variable named input of type CreateUserInput!?

easy

A. mutation createUser($input: CreateUserInput!) { ... }

B. query createUser(input: CreateUserInput!) { ... }

C. mutation createUser(input CreateUserInput!) { ... }

D. mutation createUser($input CreateUserInput!) { ... }

Solution

1. Step 1: Recall mutation syntax with variables

   Variables in GraphQL mutations start with $ and have a colon before the type.

2. Step 2: Check each option

   mutation createUser($input: CreateUserInput!) { ... } correctly uses $input: CreateUserInput!. Others miss $ or colon.

3. Final Answer:

   mutation createUser($input: CreateUserInput!) { ... } -> Option A

4. Quick Check:

   Variables need $ and colon [OK]

Hint: Variables start with $ and use colon before type [OK]

Common Mistakes:

• Omitting $ before variable name
• Missing colon between variable and type
• Using query instead of mutation keyword

3. Given this mutation:

mutation AddBook($book: BookInput!) {
  addBook(input: $book) {
    id
    title
  }
}

What fields will the server return after running this mutation?

medium

A. Only the input object sent

B. All fields of the book including author and publishedYear

C. No fields, mutation returns nothing

D. Only the id and title of the new book

Solution

1. Step 1: Identify requested return fields

   The mutation requests id and title fields inside addBook.

2. Step 2: Understand GraphQL response

   GraphQL returns only the fields explicitly requested, so only id and title are returned.

3. Final Answer:

   Only the id and title of the new book -> Option D

4. Quick Check:

   Requested fields = returned fields [OK]

Hint: Returned fields match exactly requested fields in mutation body [OK]

Common Mistakes:

• Assuming all fields return by default
• Expecting input object to be returned
• Thinking mutation returns no data

4. Identify the error in this mutation:

mutation CreatePost($post: PostInput!) {
  createPost(post: $post) {
    id
    content
  }
}

Assuming the server expects the input argument to be named input, not post.

medium

A. The mutation keyword should be query

B. The variable $post should be $input

C. The argument name post should be input

D. The return fields id and content are invalid

Solution

1. Step 1: Check argument name in mutation call

   The mutation calls createPost(post: $post), but server expects input argument.

2. Step 2: Correct argument name

   Changing post to input matches server expectation and fixes error.

3. Final Answer:

   The argument name post should be input -> Option C

4. Quick Check:

   Argument names must match server schema [OK]

Hint: Match argument names exactly as server expects [OK]

Common Mistakes:

• Using wrong argument name in mutation call
• Confusing variable name with argument name
• Changing mutation keyword incorrectly

5. You want to create a mutation to add a new user with fields name and email. Which mutation correctly uses input variables and requests the new user's id and email in the response?

hard

A. mutation AddUser($input: UserInput!) { addUser(input: $input) { id email } }

B. mutation AddUser(input: UserInput!) { addUser(input: input) { id email } }

C. mutation AddUser($user: UserInput!) { addUser(user: $user) { name email } }

D. mutation AddUser($input: UserInput!) { addUser(input: $input) { name } }

Solution

1. Step 1: Check variable declaration and usage

   mutation AddUser($input: UserInput!) { addUser(input: $input) { id email } } correctly declares $input: UserInput! and uses it as input: $input.

2. Step 2: Verify requested return fields

   mutation AddUser($input: UserInput!) { addUser(input: $input) { id email } } requests id and email, matching the question requirement.

3. Final Answer:

   mutation AddUser($input: UserInput!) { addUser(input: $input) { id email } } -> Option A

4. Quick Check:

   Correct variable and requested fields = mutation AddUser($input: UserInput!) { addUser(input: $input) { id email } } [OK]

Hint: Use $variable and request needed fields explicitly [OK]

Common Mistakes:

• Omitting $ in variable declaration or usage
• Requesting wrong fields in response
• Using wrong argument names