Input validation patterns in GraphQL - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ query_result

intermediate

What is the result of this GraphQL query with input validation?

Given the following GraphQL schema snippet that validates an input argument age to be a positive integer, what will be the result of this query?

type Query {
  user(age: Int!): String
}

# Resolver logic:
# if age <= 0, return error "Invalid age"
# else return "User age is <age>"

Query:

{ user(age: -5) }

A Error: age must be an integer

B User age is -5

C null

D Error: Invalid age

💡 Hint

Think about how the resolver handles invalid input values.

The resolver checks if the age is less than or equal to zero and returns an error message. Since -5 is invalid, it returns "Error: Invalid age".

📝 Syntax

intermediate

Which input validation directive syntax is correct in GraphQL?

Choose the correct syntax to validate that a string input email matches a simple email pattern using a custom directive @pattern.

A input UserInput { email: String! @pattern(regex: "^[^@\s]+@[^@\s]+\.[^@\s]+$") }

B input UserInput { email: String! @pattern(value: "^[^@\s]+@[^@\s]+\.[^@\s]+$") }

C input UserInput { email: String! @validate(regex: "^[^@\s]+@[^@\s]+\.[^@\s]+$") }

D input UserInput { email: String! @pattern("^[^@\s]+@[^@\s]+\.[^@\s]+$") }

💡 Hint

Look for the correct argument name and syntax for directives.

The directive uses the argument name regex with colon syntax. Option A matches this pattern correctly.

🧠 Conceptual

advanced

Why is input validation important in GraphQL APIs?

Which of the following is the best reason to implement input validation in GraphQL APIs?

A To prevent invalid or malicious data from causing errors or security issues

B To make queries run faster by skipping validation

C To allow clients to send any data without restrictions

D To reduce the size of the GraphQL schema

💡 Hint

Think about security and data integrity.

Input validation helps ensure only valid data is processed, preventing errors and security vulnerabilities.

🔧 Debug

advanced

Identify the error in this GraphQL input validation resolver

Consider this resolver function for a mutation that validates a username length:

async function createUser(parent, args) {
  if (args.username.length < 3) {
    throw new Error("Username too short");
  }
  // create user logic
  return { id: 1, username: args.username };
}

What error will occur if args.username is null?

A No error, user created successfully

B Error: Username too short

C TypeError: Cannot read property 'length' of null

D SyntaxError: Unexpected token

💡 Hint

What happens when you try to access .length of null?

Accessing length on null causes a TypeError because null has no properties.

❓ optimization

expert

How to optimize input validation for nested GraphQL inputs?

You have a mutation that accepts a nested input object with multiple fields requiring validation. Which approach optimizes validation performance and maintainability?

A Validate all fields manually inside the resolver function with nested if statements

B Use reusable custom scalar types and directives for validation on each field

C Skip validation and trust client inputs to reduce server load

D Validate only the top-level input object and ignore nested fields

💡 Hint

Think about reusability and separation of concerns.

Using custom scalars and directives allows declarative, reusable validation close to the schema, improving performance and maintainability.