Type definitions in GraphQL - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a type definition in GraphQL?

A type definition in GraphQL describes the shape of data by defining fields and their data types. It tells the server what kind of data clients can query or mutate.

beginner

What does the type keyword do in GraphQL?

The type keyword defines a new object type with a set of fields and their types. For example, type User { id: ID!, name: String } defines a User type with id and name fields.

intermediate

Explain the difference between type and input in GraphQL type definitions.

type defines the shape of data returned by queries or mutations, while input defines the shape of data sent as arguments to mutations or queries.

beginner

What does the exclamation mark ! mean in a GraphQL type definition?

The exclamation mark ! means the field is non-nullable, so it must always have a value and cannot be null.

beginner

How do you define a list of strings in a GraphQL type definition?

You define a list of strings using square brackets: [String]. For example, tags: [String] means the tags field is a list of strings.

Which keyword is used to define a new object type in GraphQL?

A type

B input

C schema

D query

The type keyword defines a new object type with fields.

What does String! mean in a GraphQL type definition?

A A non-nullable string

B An optional string

C A list of strings

D A nullable string

The exclamation mark ! means the string cannot be null.

Which type is used to define input data for mutations?

A type

B input

C enum

D scalar

input types define the shape of data sent as arguments.

How do you define a list of integers in GraphQL?

A list<Int>

B Int[]

C [Int]

D array<Int>

Lists are defined with square brackets, e.g., [Int].

What does this GraphQL type definition mean? type Book { title: String, pages: Int! }

A Both title and pages are optional

B title is required, pages is optional

C Both title and pages are required

D title is optional, pages is required

Without !, fields are nullable (optional). pages: Int! means pages is required.

Describe what a GraphQL type definition is and why it is important.

Think about how you tell a friend what information you want from them.

Explain the difference between type and input in GraphQL.

One is for output, the other for input.

Practice

1. What is the main purpose of type definitions in GraphQL?

easy

A. To describe the shape and types of data clients can request

B. To execute database queries directly

C. To style the user interface of a GraphQL client

D. To store data permanently in the server

Solution

1. Step 1: Understand the role of type definitions

   Type definitions specify what data types exist and how data is structured in GraphQL.

2. Step 2: Identify what clients use type definitions for

   Clients use type definitions to know what data they can ask for and how it will look.

3. Final Answer:

   To describe the shape and types of data clients can request -> Option A

4. Quick Check:

   Type definitions = Describe data shape [OK]

Hint: Type definitions describe data structure, not execution or styling [OK]

Common Mistakes:

• Confusing type definitions with query execution
• Thinking type definitions style UI
• Assuming type definitions store data

2. Which of the following is the correct way to define a simple GraphQL object type named Book with a title field of type String?

easy

A. define Book { title: String }

B. object Book { title: String }

C. Book type { title: String }

D. type Book { title: String }

Solution

1. Step 1: Recall GraphQL syntax for object types

   GraphQL uses the keyword type followed by the type name and fields in braces.

2. Step 2: Match the correct syntax

   type Book { title: String } matches the correct syntax: type Book { title: String }.

3. Final Answer:

   type Book { title: String } -> Option D

4. Quick Check:

   Object type syntax = type Name { fields } [OK]

Hint: Remember: 'type' keyword defines object types in GraphQL [OK]

Common Mistakes:

• Using 'object' instead of 'type'
• Placing 'type' after the name
• Using 'define' keyword which is invalid

3. Given the following GraphQL type definition:

type User {
  id: ID!
  name: String
  age: Int
}

Which of these queries will return the name and age fields of a user?

medium

A. { user { id name age } }

B. { user { name age } }

C. { user { id } }

D. { user { age id } }

Solution

1. Step 1: Identify requested fields in each query

   We want only name and age fields returned.

2. Step 2: Check which query requests exactly those fields

   { user { name age } } requests name and age only, matching the requirement.

3. Final Answer:

   { user { name age } } -> Option B

4. Quick Check:

   Query fields = name and age only [OK]

Hint: Select only needed fields inside braces after type name [OK]

Common Mistakes:

• Including extra fields like 'id' when not asked
• Requesting fields in wrong order (order doesn't matter but distracts)
• Missing required fields if needed

4. Identify the error in this GraphQL type definition:

type Product {
  id: ID
  price: Float!
  name: String!
  description: String
  price: Int
}

medium

A. Missing exclamation mark on 'id' field

B. Incorrect type 'Float!' for price

C. Duplicate field name 'price' with different types

D. Description field cannot be optional

Solution

1. Step 1: Review all fields for correctness

   Notice that 'price' is declared twice with different types: Float! and Int.

2. Step 2: Understand GraphQL rules on field names

   Field names must be unique within a type; duplicates cause errors.

3. Final Answer:

   Duplicate field name 'price' with different types -> Option C

4. Quick Check:

   Duplicate fields cause errors [OK]

Hint: Check for repeated field names in type definitions [OK]

Common Mistakes:

• Ignoring duplicate field names
• Thinking missing '!' is always an error
• Assuming optional fields are invalid

5. You want to define a GraphQL type Order that includes an id (non-null ID), a list of items (each an Item type), and a total price (non-null Float). Which is the correct type definition?

hard

A. type Order { id: ID! items: [Item!]! total: Float! }

B. type Order { id: ID items: Item total: Float }

C. type Order { id: ID! items: [Item]! total: Float! }

D. type Order { id: ID! items: [Item!] total: Float }

Solution

1. Step 1: Analyze each field requirement

   'id' must be non-null ID, 'items' is a non-null list of non-null Item, 'total' is non-null Float.

2. Step 2: Match the correct syntax

   type Order { id: ID! items: [Item!]! total: Float! } correctly uses ID!, [Item!]! (list non-null and items non-null), and Float!.

3. Final Answer:

   type Order { id: ID! items: [Item!]! total: Float! } -> Option A

4. Quick Check:

   Non-null fields and list syntax correct [OK]

Hint: Use [Type!]! for non-null list of non-null items [OK]

Common Mistakes:

• Missing non-null markers (!)
• Using list without non-null item type
• Confusing list syntax with single type