Update mutation pattern in GraphQL - Mini Project: Build & Apply

Create a GraphQL Update Mutation

📖 Scenario: You are building a simple GraphQL API for a bookstore. You want to allow users to update the details of a book, such as its title and author.

🎯 Goal: Build a GraphQL updateBook mutation that updates a book's id, title, and author fields.

📋 What You'll Learn

Create a GraphQL input type called UpdateBookInput with fields id, title, and author.

Define a mutation called updateBook that takes an input argument of type UpdateBookInput.

The mutation should return the updated book's id, title, and author.

Use the exact names UpdateBookInput, updateBook, and input in your code.

💡 Why This Matters

🌍 Real World

GraphQL update mutations are used in APIs to allow clients to modify existing data records safely and clearly.

💼 Career

Understanding how to write update mutations is essential for backend developers working with GraphQL APIs in real-world applications.

1

Define the UpdateBookInput input type

Create a GraphQL input type called UpdateBookInput with the fields id of type ID!, title of type String, and author of type String.

GraphQL

# Define the UpdateBookInput input type
# Your code here

Hint

Use the input keyword to define an input type with the specified fields.

2

Add the updateBook mutation field

Add a mutation field called updateBook that takes an argument named input of type UpdateBookInput!.

GraphQL

input UpdateBookInput {
  id: ID!
  title: String
  author: String
}

# Add the updateBook mutation field below
# Your code here

Hint

Define a Mutation type and add the updateBook field with the correct argument.

3

Define the Book type

Define a GraphQL type called Book with fields id of type ID!, title of type String, and author of type String.

GraphQL

input UpdateBookInput {
  id: ID!
  title: String
  author: String
}

type Mutation {
  updateBook(input: UpdateBookInput!): Book
}

# Define the Book type below
# Your code here

Hint

Use the type keyword to define the Book type with the specified fields.

4

Complete the update mutation schema

Ensure the full schema includes the UpdateBookInput input type, the Book type, and the Mutation type with the updateBook mutation returning a Book.

GraphQL

input UpdateBookInput {
  id: ID!
  title: String
  author: String
}

type Mutation {
  updateBook(input: UpdateBookInput!): Book
}

type Book {
  id: ID!
  title: String
  author: String
}

# Finalize the schema if needed
# Your code here

Hint

Review your schema to confirm all parts are included and correctly linked.

Practice

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

easy

A. To create new data records

B. To change existing data by specifying an ID and new values

C. To delete data from the database

D. To fetch data without any changes

Solution

1. Step 1: Understand the role of update mutations

   Update mutations modify existing records by identifying them and applying new values.

2. Step 2: Differentiate from other mutation types

   Delete mutations remove data, create mutations add new data, and queries fetch data without changes.

3. Final Answer:

   To change existing data by specifying an ID and new values -> Option B

4. Quick Check:

   Update mutation = change existing data [OK]

Hint: Update mutations modify existing records by ID [OK]

Common Mistakes:

• Confusing update with create or delete mutations
• Thinking update fetches data without changes
• Assuming update creates new records

2. Which of the following is the correct syntax for an update mutation in GraphQL?

easy

A. mutation { updateUser(id: "123", input: {name: "Alice"}) { id name } }

B. mutation { createUser(id: "123", input: {name: "Alice"}) { id name } }

C. query { updateUser(id: "123", input: {name: "Alice"}) { id name } }

D. mutation { deleteUser(id: "123") { id name } }

Solution

1. Step 1: Identify the mutation keyword and operation

   Update mutations use the mutation keyword and specify the update operation with an ID and input object.

2. Step 2: Check the options for correct mutation syntax

   mutation { updateUser(id: "123", input: {name: "Alice"}) { id name } } uses mutation with updateUser and input fields correctly; others use wrong operation or query keyword.

3. Final Answer:

   mutation { updateUser(id: "123", input: {name: "Alice"}) { id name } } -> Option A

4. Quick Check:

   Update mutation syntax = mutation + update operation + input [OK]

Hint: Update mutations use 'mutation' keyword with update operation [OK]

Common Mistakes:

• Using 'query' instead of 'mutation'
• Using create or delete operation instead of update
• Missing input object for new values

3. Given this mutation:

mutation { updatePost(id: "5", input: {title: "New Title"}) { id title content } }

What will be the output if the post with ID 5 exists and has content "Old content"?

medium

A. { "data": { "updatePost": null } }

B. { "data": { "updatePost": { "id": "5", "title": "Old Title", "content": "Old content" } } }

C. { "data": { "updatePost": { "id": "5", "title": "New Title", "content": "Old content" } } }

D. Error: Post with ID 5 not found

Solution

1. Step 1: Understand the mutation effect

   The mutation updates the post with ID 5, changing only the title to "New Title" while keeping other fields unchanged.

2. Step 2: Predict the returned data

   The response includes the updated title and the unchanged content "Old content" along with the ID.

3. Final Answer:

   { "data": { "updatePost": { "id": "5", "title": "New Title", "content": "Old content" } } } -> Option C

4. Quick Check:

   Update mutation returns updated fields plus unchanged fields [OK]

Hint: Update changes specified fields, others remain same [OK]

Common Mistakes:

• Assuming all fields reset or become null
• Expecting error when post exists
• Ignoring unchanged fields in output

4. Identify the error in this update mutation:

mutation { updateUser(input: {name: "Bob"}) { id name } }

medium

A. Missing the ID argument to specify which user to update

B. Input object should be named 'data' instead of 'input'

C. Mutation keyword should be 'query' instead of 'mutation'

D. Cannot update the 'name' field

Solution

1. Step 1: Check required arguments for update mutation

   Update mutations require an ID to identify the record to update.

2. Step 2: Analyze the given mutation

   The mutation lacks the ID argument, so it cannot know which user to update.

3. Final Answer:

   Missing the ID argument to specify which user to update -> Option A

4. Quick Check:

   Update mutation must include ID argument [OK]

Hint: Always include ID to update specific record [OK]

Common Mistakes:

• Omitting the ID argument
• Confusing input object name
• Using 'query' instead of 'mutation'

5. You want to update a user's email and phone number but only if the phone number is provided. Which mutation pattern correctly handles this conditional update?

mutation UpdateUser($id: ID!, $email: String!, $phone: String) {
  updateUser(id: $id, input: {email: $email, phone: $phone}) {
    id
    email
    phone
  }
}

hard

A. Create separate mutations for email and phone updates

B. Always send phone field with empty string if no update needed

C. Use optional input fields and send null for phone if not updating

D. Remove phone field from input object when not updating

Solution

1. Step 1: Understand conditional updates in GraphQL

   To update only provided fields, omit fields not meant to be changed from the input object.

2. Step 2: Analyze options for handling optional phone

   Sending null or empty string may overwrite data; omitting the phone field avoids unintended changes.

3. Final Answer:

   Remove phone field from input object when not updating -> Option D

4. Quick Check:

   Omit fields to keep existing values unchanged [OK]

Hint: Omit fields to avoid overwriting unchanged data [OK]

Common Mistakes:

• Sending null overwrites existing data
• Using empty string instead of omitting field
• Creating unnecessary multiple mutations