Object types in GraphQL - Mini Project: Build & Apply

Building a GraphQL Object Type for a Bookstore

📖 Scenario: You are creating a simple GraphQL API for a bookstore. You want to define the structure of the data for books so that clients can query book details easily.

🎯 Goal: Build a GraphQL Book object type with specific fields to represent books in the bookstore.

📋 What You'll Learn

Create a GraphQL object type named Book

Add fields id, title, author, and publishedYear with correct types

Use ID! type for id to uniquely identify each book

Use String! type for title and author

Use Int type for publishedYear which can be null if unknown

💡 Why This Matters

🌍 Real World

GraphQL object types define the shape of data clients can request from APIs, making data fetching clear and efficient.

💼 Career

Understanding GraphQL schemas is essential for backend developers and API designers working with modern web applications.

1

Define the Book object type

Create a GraphQL object type called Book with no fields yet.

GraphQL

type Book {
  # Your code here
}

Hint

Start by writing type Book { } to define the object type.

2

Add the id field

Inside the Book type, add a field called id with type ID!.

GraphQL

type Book {
  # Add the id field here
}

Hint

The id field should be non-nullable and use the ID! type.

3

Add title and author fields

Add two more fields inside Book: title and author, both with type String!.

GraphQL

type Book {
  id: ID!
  # Add title and author fields here
}

Hint

Both title and author are required strings, so use String!.

4

Add optional publishedYear field

Add a field called publishedYear with type Int (nullable) inside the Book type.

GraphQL

type Book {
  id: ID!
  title: String!
  author: String!
  # Add publishedYear field here
}

Hint

The publishedYear can be missing, so do not add an exclamation mark.

Practice

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

easy

A. To execute database queries directly

B. To create user interface components

C. To store data permanently

D. To define the shape and fields of data objects

Solution

1. Step 1: Understand the role of Object types in GraphQL

   Object types describe what fields an object has and their types, shaping the data structure.

2. Step 2: Differentiate from other concepts

   Object types do not execute queries, store data, or create UI components; they only define data shapes.

3. Final Answer:

   To define the shape and fields of data objects -> Option D

4. Quick Check:

   Object type = data shape definition [OK]

Hint: Object types describe data fields and their types [OK]

Common Mistakes:

• Confusing object types with query execution
• Thinking object types store data
• Mixing object types with UI components

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

easy

A. object Book { title: String }

B. type Book { title: String }

C. Book type { title: String }

D. define Book { title: String }

Solution

1. Step 1: Recall GraphQL object type syntax

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

2. Step 2: Check each option

   Only type Book { title: String } uses the correct syntax: type Book { title: String }. Others use invalid keywords.

3. Final Answer:

   type Book { title: String } -> Option B

4. Quick Check:

   Keyword 'type' + name + fields = correct syntax [OK]

Hint: Use 'type' keyword to define object types [OK]

Common Mistakes:

• Using 'object' or 'define' instead of 'type'
• Placing type name after 'type' incorrectly
• Missing braces around fields

3. Given the GraphQL object type definition:

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

What is the expected result of querying:

{ user { id name } }

?

medium

A. Returns user object with only id and name fields

B. Returns user object with id, name, and age fields

C. Returns an error because age is missing

D. Returns null because query is incomplete

Solution

1. Step 1: Understand GraphQL query field selection

   GraphQL returns only the fields requested in the query, here id and name.

2. Step 2: Check if missing fields cause errors

   Missing age in query does not cause error; it is simply not returned.

3. Final Answer:

   Returns user object with only id and name fields -> Option A

4. Quick Check:

   Query fields = returned fields only [OK]

Hint: GraphQL returns only requested fields in query [OK]

Common Mistakes:

• Expecting all fields to be returned by default
• Thinking missing fields cause errors
• Assuming incomplete queries return null

4. Identify the error in this GraphQL object type definition:

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

medium

A. ID type cannot have exclamation mark

B. Missing exclamation mark on 'name' field

C. Duplicate field name 'price' with different types

D. Object type must have at least one field

Solution

1. Step 1: Review field names and types

   The field price is declared twice with different types (Float and Int), which is invalid.

2. Step 2: Check other options

   Exclamation mark on ID! is valid for non-null. Fields can be optional. Object type can have multiple fields.

3. Final Answer:

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

4. Quick Check:

   Field names must be unique in object type [OK]

Hint: Field names must be unique in object types [OK]

Common Mistakes:

• Allowing duplicate field names
• Misunderstanding non-null syntax
• Thinking object types need all fields non-null

5. You want to define a GraphQL object type Author that includes a list of Book objects. Which is the correct way to define the books field?

hard

A. books: [Book]

B. books: Book[]

C. books: List<Book>

D. books: {Book}

Solution

1. Step 1: Recall GraphQL list syntax

   GraphQL uses square brackets around a type to indicate a list, e.g., [Book].

2. Step 2: Evaluate each option

   books: [Book] uses correct GraphQL syntax. Options A, B, and C use syntax from other languages or invalid formats.

3. Final Answer:

   books: [Book] -> Option A

4. Quick Check:

   Lists use square brackets in GraphQL [OK]

Hint: Use square brackets for lists in GraphQL types [OK]

Common Mistakes:

• Using array syntax from other languages
• Using curly braces instead of brackets
• Confusing list syntax with generics