Mutation syntax in GraphQL - Mini Project: Build & Apply

GraphQL Mutation Syntax Basics

📖 Scenario: You are building a simple contact list app. You want to add new contacts to your list using GraphQL mutations.

🎯 Goal: Learn how to write a basic GraphQL mutation to add a new contact with a name and phone number.

📋 What You'll Learn

Create a mutation named addContact that accepts name and phone as inputs

Return the id, name, and phone of the newly added contact

Use proper GraphQL mutation syntax with variables

💡 Why This Matters

🌍 Real World

GraphQL mutations are used to change data on servers, such as adding or updating contacts in an app.

💼 Career

Understanding mutation syntax is essential for backend and frontend developers working with GraphQL APIs to manage data.

1

Define the mutation operation with variables

Write the first line of a GraphQL mutation named AddContact that takes two variables: $name of type String! and $phone of type String!.

GraphQL

# Your code here
mutation AddContact($name: String!, $phone: String!) {

Hint

Start with the keyword mutation, then the mutation name, and declare variables with their types inside parentheses.

2

Call the addContact mutation with variables

Inside the mutation block, call addContact passing name: $name and phone: $phone as arguments.

GraphQL

mutation AddContact($name: String!, $phone: String!) {
  addContact(name: $name, phone: $phone) {
    # Your code here
  }
}

Hint

Use the mutation field name addContact and pass the variables as arguments.

3

Select fields to return from the mutation

Inside the addContact block, select the fields id, name, and phone to be returned.

GraphQL

mutation AddContact($name: String!, $phone: String!) {
  addContact(name: $name, phone: $phone) {
    # Your code here
  }
}

Hint

List the fields you want back from the mutation inside its curly braces.

4

Close the mutation block

Add the closing curly brace } to close the mutation operation.

GraphQL

mutation AddContact($name: String!, $phone: String!) {
  addContact(name: $name, phone: $phone) {
    id
    name
    phone
  }
  # Your code here
}

Hint

Make sure all opened curly braces are properly closed.

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