Validation errors in GraphQL - Mini Project: Build & Apply

Handling Validation Errors in GraphQL

📖 Scenario: You are building a simple GraphQL API for a bookstore. You want to ensure that when users add new books, the input data is validated properly to avoid errors like missing required fields or invalid data types.

🎯 Goal: Create a GraphQL schema with a Book type and a mutation addBook that validates input fields. Implement validation rules to catch errors such as missing title or author and invalid year values.

📋 What You'll Learn

Define a Book type with fields id, title, author, and year

Create an input type BookInput with the same fields except id

Add a mutation addBook that accepts BookInput and returns a Book

Implement validation to check that title and author are not empty

Validate that year is a positive integer

Return clear validation error messages when input is invalid

💡 Why This Matters

🌍 Real World

GraphQL APIs often require input validation to ensure data integrity and provide clear error messages to clients.

💼 Career

Understanding how to handle validation errors in GraphQL is essential for backend developers building robust APIs.

1

Define the Book type and BookInput input type

Write the GraphQL schema to define a Book type with fields id (ID!), title (String!), author (String!), and year (Int). Also define an input type BookInput with fields title (String!), author (String!), and year (Int).

GraphQL

# Define the Book type and BookInput input type
# Your code here

Hint

Use type to define the Book object and input to define BookInput. Mark required fields with !.

2

Add the addBook mutation to the schema

Add a mutation called addBook that takes one argument input of type BookInput! and returns a Book.

GraphQL

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

input BookInput {
  title: String!
  author: String!
  year: Int
}

# Add the addBook mutation below
# Your code here

Hint

Define a Mutation type with the addBook mutation accepting input of type BookInput!.

3

Implement validation logic for addBook mutation

In your resolver for addBook, add validation to check that input.title and input.author are not empty strings, and that input.year is a positive integer if provided. Return validation error messages if any check fails.

GraphQL

# Implement resolver validation logic for addBook mutation
# Your code here

Hint

Use throw new Error() to return validation errors. Check for empty strings with trim() and validate year as a positive number.

4

Complete the schema with Query type and export

Add a Query type with a books field that returns a list of Book. Export the schema and resolvers for use in your GraphQL server.

GraphQL

Hint

Define a Query type with a books field returning a list of Book. Export typeDefs and resolvers for your server.