Mutation syntax in GraphQL - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a mutation in GraphQL?

A mutation is a special type of GraphQL operation used to change data on the server, like creating, updating, or deleting records.

beginner

How do you start writing a mutation in GraphQL?

You start with the keyword mutation, followed by the mutation name and the fields you want to change or return.

intermediate

What is the purpose of variables in a GraphQL mutation?

Variables let you pass dynamic values into a mutation, making it reusable and flexible without changing the mutation code itself.

beginner

Explain the structure of a simple GraphQL mutation to add a new user with name and email.

A mutation includes the mutation keyword, a mutation name, input arguments like name and email, and the fields you want back, for example:

mutation {
  addUser(name: "Alice", email: "[e-mail]") {
    id
    name
  }
}

intermediate

Why do mutations usually return data after execution?

Returning data after a mutation confirms the change and provides updated information, like the new record's ID or updated fields.

Which keyword starts a GraphQL mutation?

A change

B mutation

C update

D query

The keyword mutation is used to start a mutation operation in GraphQL.

What does a GraphQL mutation typically do?

A Fetch data without changes

B Delete the entire database

C Change data on the server

D Only update client-side data

Mutations are designed to change data on the server, such as creating, updating, or deleting records.

How do you pass dynamic values into a mutation?

A Using variables

B Hardcoding values

C Using comments

D Using fragments

Variables allow you to pass dynamic values into mutations, making them reusable.

What is the correct way to request the ID of a newly created user in a mutation?

A Use a special <code>getId</code> keyword

B Use a separate query after mutation

C Mutations cannot return fields

D Include <code>id</code> in the mutation's return fields

You include the id field in the mutation's return selection to get it back after the mutation.

Which of these is NOT a typical use of a GraphQL mutation?

A Fetching a list of items

B Updating existing data

C Creating a new record

D Deleting a record

Fetching data is done with queries, not mutations.

Describe the basic syntax of a GraphQL mutation and how it differs from a query.

Think about how you tell the server to change data instead of just asking for it.

Explain why variables are useful in GraphQL mutations and give an example of their use.

Variables help avoid rewriting the mutation for different inputs.

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