Input arguments for mutations in GraphQL

Introduction

Input arguments let you send data to change or add information in a database using mutations.

When you want to add a new user with details like name and email.

When you need to update a product's price or description.

When deleting an item by specifying its ID.

When creating a new post with a title and content.

When changing a user's password securely.

Syntax

GraphQL

mutation MutationName($inputName: InputType!) {
  mutationField(input: $inputName) {
    returnField
  }
}

Input arguments are defined with a $ sign and a type before the mutation body.

The exclamation mark (!) means the input is required.

Examples

This mutation adds a user by passing a userInput object with user details.

GraphQL

mutation AddUser($userInput: UserInput!) {
  addUser(input: $userInput) {
    id
    name
  }
}

This mutation updates a product's price using two input arguments: productId and price.

GraphQL

mutation UpdateProduct($productId: ID!, $price: Float!) {
  updateProduct(id: $productId, price: $price) {
    id
    price
  }
}

Sample Program

This mutation creates a new post by sending a postInput object with title and content.

GraphQL

mutation CreatePost($postInput: PostInput!) {
  createPost(input: $postInput) {
    id
    title
    content
  }
}

# Variables:
# {
#   "postInput": {
#     "title": "My First Post",
#     "content": "Hello, this is my first post!"
#   }
# }

Important Notes

Always define input types in your GraphQL schema to organize input data.

Use variables to keep your mutation queries clean and reusable.

Input arguments help keep your API flexible and secure by controlling what data is sent.

Summary

Input arguments let you send data to mutations to create, update, or delete records.

They are defined with types and passed as variables for clarity and safety.

Using input arguments makes your GraphQL API easy to use and maintain.

Practice

1. What is the main purpose of input arguments in GraphQL mutations?

easy

A. To send data to create, update, or delete records

B. To define the schema of queries

C. To style the GraphQL interface

D. To fetch data without any changes

Solution

1. Step 1: Understand the role of mutations

   Mutations in GraphQL are used to change data, such as creating or updating records.

2. Step 2: Identify the use of input arguments

   Input arguments provide the data needed for these changes, like new values or identifiers.

3. Final Answer:

   To send data to create, update, or delete records -> Option A

4. Quick Check:

   Input arguments = send data for mutations [OK]

Hint: Input arguments send data to mutations for changes [OK]

Common Mistakes:

• Confusing input arguments with query filters
• Thinking input arguments style the API
• Assuming mutations fetch data only

2. Which of the following is the correct way to define an input argument for a mutation in GraphQL?

easy

A. mutation addUser(name: String!) { createUser(name: name) { id } }

B. mutation addUser($name: String!) { createUser(name: $name) { id } }

C. mutation addUser { createUser(name: String!) { id } }

D. mutation addUser($name) { createUser(name: $name) { id } }

Solution

1. Step 1: Recognize variable declaration syntax

   Input arguments must be declared with a $ prefix and type, like $name: String!.

2. Step 2: Use variables inside mutation

   Inside the mutation body, use the variable with $name to pass the value.

3. Final Answer:

   mutation addUser($name: String!) { createUser(name: $name) { id } } -> Option B

4. Quick Check:

   Variables use $name: Type! and $name inside mutation [OK]

Hint: Declare variables with $ and type, use $ inside mutation [OK]

Common Mistakes:

• Omitting $ in variable declaration
• Using type inside mutation call instead of variable
• Not specifying variable type

3. Given the mutation and variables below, what will be the returned id after execution?

mutation updateUser($id: ID!, $email: String!) { updateUser(id: $id, email: $email) { id email } }
{ "id": "123", "email": "[e-mail]" }

medium

A. "123"

B. "[e-mail]"

C. null

D. Error: Missing required fields

Solution

1. Step 1: Understand mutation input and output

   The mutation updates the user with id "123" and new email, returning the user's id and email.

2. Step 2: Identify returned id value

   The returned id is the same as the input id, which is "123".

3. Final Answer:

   "123" -> Option A

4. Quick Check:

   Returned id matches input id "123" [OK]

Hint: Returned id matches input id argument [OK]

Common Mistakes:

• Confusing returned id with email
• Assuming null if email changes
• Expecting error without missing fields

4. Identify the error in this mutation definition:

mutation deleteUser(id: ID!) { removeUser(id: id) { success } }

medium

A. removeUser field cannot have arguments

B. Variable type ID! is incorrect

C. Mutation name deleteUser is invalid

D. Missing $ before variable name in mutation definition

Solution

1. Step 1: Check variable declaration syntax

   Variables in mutation definitions must start with $, e.g., $id: ID!.

2. Step 2: Verify usage inside mutation

   Inside the mutation body, use the variable with $id, not just id.

3. Final Answer:

   Missing $ before variable name in mutation definition -> Option D

4. Quick Check:

   Variables require $ prefix in definition and usage [OK]

Hint: Always prefix variables with $ in mutation definitions [OK]

Common Mistakes:

• Omitting $ in variable declaration
• Using variable name without $ inside mutation
• Assuming mutation name must match field

5. You want to create a mutation that accepts a complex input object with fields title (String), content (String), and tags (list of Strings). Which is the correct way to define the input argument and use it in the mutation?

hard

A. type PostInput { title: String!, content: String!, tags: [String!]! }mutation createPost(post: PostInput!) { addPost(post: post) { id } }

B. input PostInput { title: String, content: String, tags: String }mutation createPost($post: PostInput) { addPost(post: $post) { id } }

C. input PostInput { title: String!, content: String!, tags: [String!]! }mutation createPost($post: PostInput!) { addPost(input: $post) { id } }

D. input PostInput { title: String!, content: String!, tags: [String] }mutation createPost($post: PostInput!) { addPost(input: post) { id } }

Solution

1. Step 1: Define input type correctly

   Use input keyword with required fields and list type: tags: [String!]! means list of non-null strings, list itself required.

2. Step 2: Declare variable and use it properly

   Declare variable with $post: PostInput! and use it as input: $post inside mutation.

3. Final Answer:

   input PostInput { title: String!, content: String!, tags: [String!]! }
   mutation createPost($post: PostInput!) { addPost(input: $post) { id } } -> Option C

4. Quick Check:

   Use input type and $variable with correct usage [OK]

Hint: Use input type and $variable with correct usage inside mutation [OK]

Common Mistakes:

• Using type instead of input for input objects
• Omitting $ in variable declaration or usage
• Incorrect list type syntax or missing non-null markers
• Passing variable without $ inside mutation