List types in GraphQL - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a List type in GraphQL?

A List type in GraphQL represents an array of values of a specific type. It allows you to return multiple items instead of just one.

beginner

How do you define a List type in a GraphQL schema?

You define a List type by wrapping the type in square brackets. For example, [String] means a list of strings.

intermediate

What does [Int!]! mean in GraphQL?

It means a non-null list of non-null integers. The list itself cannot be null, and none of the integers inside can be null.

beginner

Can a List type contain different types of values in GraphQL?

No, a List type must contain values of the same specified type. For example, [String] can only contain strings.

beginner

Why use List types in GraphQL queries?

List types let you fetch multiple related items in one query, like a list of users or posts, making data fetching efficient and organized.

How do you represent a list of strings in GraphQL schema?

A [String]

B String[]

C List<String>

D {String}

In GraphQL, list types are represented by square brackets around the type, like [String].

What does the exclamation mark (!) mean in GraphQL types?

A The value is a list

B The value is optional

C The value cannot be null

D The value is a string

An exclamation mark means the value cannot be null, ensuring it must always have a value.

Which of these is a valid GraphQL list type for non-null integers?

A [Int!]

B [Int]

C Int!

D Int[]

[Int!] means a list of integers where each integer cannot be null.

Can a GraphQL list contain different types like [String, Int]?

A Yes, lists can mix types

B No, lists must have one type only

C Only if wrapped in a union type

D Only if marked nullable

GraphQL lists must contain values of the same type; mixing types is not allowed.

What is the benefit of using list types in GraphQL queries?

A To limit query depth

B To make queries faster by skipping data

C To avoid using variables

D To fetch multiple items in one query

List types allow fetching multiple related items in a single query, improving efficiency.

Explain how to define and use List types in GraphQL schemas.

Think about how you would describe an array of items in GraphQL.

Describe the importance of List types when querying data in GraphQL.

Consider why you might want to get many records instead of just one.

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