List types in GraphQL - Mini Project: Build & Apply

GraphQL List Types Practice

📖 Scenario: You are building a simple GraphQL schema for a bookstore. You want to store a list of book titles available in the store.

🎯 Goal: Create a GraphQL schema that defines a Bookstore type with a field books that is a list of strings representing book titles.

📋 What You'll Learn

Define a GraphQL type called Bookstore

Add a field called books to Bookstore

The books field must be a list of strings

Use proper GraphQL list syntax for the books field

💡 Why This Matters

🌍 Real World

GraphQL schemas often need to represent collections of items, like lists of books, users, or products.

💼 Career

Understanding list types and nullability in GraphQL is essential for backend developers working with APIs.

1

Define the Bookstore type

Create a GraphQL type called Bookstore with no fields yet.

GraphQL

# Your code here
type Bookstore {
  # Add fields here
}

Hint

Start by writing type Bookstore { } to define the type.

2

Add the books field

Inside the Bookstore type, add a field called books with type [String] to represent a list of book titles.

GraphQL

type Bookstore {
  # Add the books field as a list of strings
}

Hint

Use square brackets [] around String to make it a list type.

3

Make the books list non-nullable

Modify the books field so that the list itself cannot be null by adding an exclamation mark ! after the list type.

GraphQL

type Bookstore {
  # Make the books list non-nullable
}

Hint

Add ! after the list type to make the list non-nullable.

4

Make the book titles non-nullable

Modify the books field so that each book title inside the list is also non-nullable by adding an exclamation mark ! after String inside the list.

GraphQL

type Bookstore {
  # Make each book title non-nullable
}

Hint

Add ! after String inside the brackets to make each item non-nullable.

Practice

1. What does a list type in GraphQL represent?
[Int] means a list of what?

easy

A. A string value

B. A single integer

C. A collection of integers

D. A boolean value

Solution

1. Step 1: Understand list notation in GraphQL

   Square brackets [] indicate a list type that holds multiple values of the same type.

2. Step 2: Interpret [Int]

   This means a list containing zero or more integers.

3. Final Answer:

   A collection of integers -> Option C

4. Quick Check:

   List type = multiple values [OK]

Hint: Square brackets mean list of that type [OK]

Common Mistakes:

• Thinking it holds a single value
• Confusing list with string or boolean
• Ignoring the brackets meaning

2. Which of the following is the correct syntax to define a list of strings in GraphQL?

easy

A. string[]

B. [String]

C. (String[])

D. {String}

Solution

1. Step 1: Recall GraphQL list syntax

   GraphQL uses square brackets [] around a type to define a list.

2. Step 2: Identify correct option

   [String] is the correct way to define a list of strings in GraphQL.

3. Final Answer:

   [String] -> Option B

4. Quick Check:

   List syntax = brackets around type [OK]

Hint: Use square brackets around type for lists [OK]

Common Mistakes:

• Using language-specific syntax like string[]
• Using parentheses or curly braces instead of brackets
• Missing brackets entirely

3. Given this GraphQL schema snippet:

type Query {
  favoriteNumbers: [Int]
}

What is a valid response for favoriteNumbers?

medium

A. {1, 2, 3}

B. 42

C. "[1, 2, 3]"

D. [1, 2, 3]

Solution

1. Step 1: Understand the field type

   favoriteNumbers is a list of integers, so the response must be a list (array) of numbers.

2. Step 2: Check each option

   [1, 2, 3] is a list of integers. 42 is a single integer, not a list. "[1, 2, 3]" is a string, not a list. {1, 2, 3} uses curly braces which is invalid syntax.

3. Final Answer:

   [1, 2, 3] -> Option D

4. Quick Check:

   List field returns list value [OK]

Hint: List fields return arrays, not single values [OK]

Common Mistakes:

• Returning a single value instead of a list
• Returning a string instead of a list
• Using wrong brackets for lists

4. Identify the error in this GraphQL list type declaration:

type User {
  tags: [String
}

medium

A. Missing closing bracket "]" for the list type

B. List types cannot hold strings

C. Square brackets should be replaced with parentheses

D. Field name cannot be "tags"

Solution

1. Step 1: Check list type syntax

   List types require both opening and closing square brackets around the type.

2. Step 2: Locate syntax error

   The closing bracket "]" is missing after String, causing a syntax error.

3. Final Answer:

   Missing closing bracket "]" for the list type -> Option A

4. Quick Check:

   List syntax needs matching brackets [OK]

Hint: Always close brackets in list types [OK]

Common Mistakes:

• Forgetting the closing bracket
• Using wrong brackets like parentheses
• Thinking list can't hold strings

5. You want to define a GraphQL field that can return null or a list of non-null integers, but the list itself can be empty. Which type declaration is correct?

hard

A. [Int!]

B. [Int]!

C. [Int!]!

D. Int!

Solution

1. Step 1: Understand non-null and list syntax

   Int! means non-null integer, [Int!] means list of non-null integers, list itself can be null or empty.

2. Step 2: Analyze options

   [Int!]: List of non-null integers, list nullable (can be empty).[Int]!: Non-null list of nullable integers.[Int!]!: Non-null list of non-null integers (list cannot be null).Int!: Single non-null integer, not a list.

3. Final Answer:

   [Int!] -> Option A

4. Quick Check:

   Non-null items inside nullable list = [Int!] [OK]

Hint: Non-null items inside list use [Type!] [OK]

Common Mistakes:

• Making list itself non-null when it should be nullable
• Confusing non-null item vs non-null list
• Using single type instead of list