Mutation syntax in GraphQL

Introduction

Mutations let you change data in a database, like adding or updating information.

When you want to add a new user to a system.

When updating a product's price in an online store.

When deleting a comment from a blog post.

When changing a user's password.

When submitting a form that saves data.

Syntax

GraphQL

mutation MutationName {
  mutationFieldName(input: InputType) {
    returnedField1
    returnedField2
  }
}

Start with the keyword mutation followed by an optional name.

Inside braces, call the mutation field with input data, then specify what data you want back.

Examples

Adds a new user named Alice and asks for the new user's id and name in response.

GraphQL

mutation {
  addUser(name: "Alice", age: 30) {
    id
    name
  }
}

Updates the price of a product with id 123 and returns the updated id and price.

GraphQL

mutation UpdatePrice {
  updateProductPrice(id: "123", price: 19.99) {
    id
    price
  }
}

Deletes a comment by id and returns if it was successful and a message.

GraphQL

mutation {
  deleteComment(id: "456") {
    success
    message
  }
}

Sample Program

This mutation adds a new book with a title and author, then returns the book's id, title, and author.

GraphQL

mutation {
  createBook(title: "Learn GraphQL", author: "Sam") {
    id
    title
    author
  }
}

Important Notes

Mutations always change data, unlike queries which only read data.

You can request specific fields in the response to get only what you need.

Give your mutation a name to help with debugging and tracking.

Summary

Mutations let you add, update, or delete data in GraphQL.

Use the mutation keyword followed by the mutation call and requested return fields.

Always specify what data you want back after the mutation runs.

Practice

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

easy

A. To define the data schema

B. To fetch data without changing anything

C. To create a new GraphQL server

D. To change data on the server like adding, updating, or deleting records

Solution

1. Step 1: Understand GraphQL operations

   GraphQL has queries to fetch data and mutations to change data.

2. Step 2: Identify mutation role

   Mutations are used to add, update, or delete data on the server.

3. Final Answer:

   To change data on the server like adding, updating, or deleting records -> Option D

4. Quick Check:

   Mutation = change data [OK]

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

Common Mistakes:

• Confusing mutations with queries
• Thinking mutations define schema
• Assuming mutations create servers

2. Which of the following is the correct basic syntax to start a mutation in GraphQL?

easy

A. mutation { addUser(name: "Alice") { id name } }

B. query { addUser(name: "Alice") { id name } }

C. mutation addUser { name: "Alice" }

D. addUser mutation { name: "Alice" }

Solution

1. Step 1: Recognize mutation keyword usage

   Mutations start with the keyword mutation followed by braces containing the mutation call.

2. Step 2: Check correct structure

   mutation { addUser(name: "Alice") { id name } } correctly uses mutation { addUser(...) { ... } } syntax.

3. Final Answer:

   mutation { addUser(name: "Alice") { id name } } -> Option A

4. Quick Check:

   Mutation starts with 'mutation' keyword and braces [OK]

Hint: Mutation always starts with 'mutation' keyword and braces [OK]

Common Mistakes:

• Using 'query' instead of 'mutation'
• Placing mutation name before 'mutation' keyword
• Missing braces around mutation call

3. Given the mutation below, what will be returned?

mutation {
  createPost(title: "Hello") {
    id
    title
  }
}

medium

A. No return data because no fields requested

B. { "data": { "createPost": null } }

C. { "data": { "createPost": { "id": 1, "title": "Hello" } } }

D. Syntax error: missing fields

Solution

1. Step 1: Analyze mutation call and requested fields

   The mutation calls createPost with title "Hello" and requests id and title fields back.

2. Step 2: Understand expected return

   The server returns the new post's id and title as requested.

3. Final Answer:

   { "data": { "createPost": { "id": 1, "title": "Hello" } } } -> Option C

4. Quick Check:

   Requested fields returned in data [OK]

Hint: Requested fields inside mutation braces are returned [OK]

Common Mistakes:

• Expecting no return data
• Confusing syntax error with correct syntax
• Ignoring requested fields in response

4. Identify the error in this mutation:

mutation {
  updateUser(id: 5, name: "Bob")
}

medium

A. Missing requested return fields after mutation call

B. Wrong keyword, should be 'query' instead of 'mutation'

C. Mutation name 'updateUser' is invalid

D. Extra parentheses around arguments

Solution

1. Step 1: Check mutation syntax

   Mutation calls must specify which fields to return inside braces after the call.

2. Step 2: Identify missing return fields

   This mutation lacks braces with requested fields after updateUser, causing syntax error.

3. Final Answer:

   Missing requested return fields after mutation call -> Option A

4. Quick Check:

   Mutations must request return fields [OK]

Hint: Always request fields after mutation call in braces [OK]

Common Mistakes:

• Omitting return fields
• Using 'query' keyword for mutations
• Misplacing parentheses

5. You want to delete a user by ID and get back the deleted user's name and email. Which mutation is correct?

hard

A. mutation deleteUser(id: 10) { name email }

B. mutation { deleteUser(id: 10) { name email } }

C. mutation { deleteUser(id: 10) }

D. deleteUser mutation { id: 10, name, email }

Solution

1. Step 1: Confirm mutation keyword and structure

   Mutation must start with mutation keyword followed by braces containing the mutation call.

2. Step 2: Check mutation call and requested fields

   mutation { deleteUser(id: 10) { name email } } correctly calls deleteUser with id: 10 and requests name and email fields.

3. Final Answer:

   mutation { deleteUser(id: 10) { name email } } -> Option B

4. Quick Check:

   Correct mutation syntax with requested return fields [OK]

Hint: Mutation call inside braces with requested fields in nested braces [OK]

Common Mistakes:

• Placing mutation name after keyword incorrectly
• Not requesting return fields
• Using wrong keyword order