Validation with Joi in NestJS - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

What happens when a NestJS controller uses Joi validation and receives invalid data?

Consider a NestJS controller method that uses Joi to validate incoming request data. If the data does not match the Joi schema, what will be the behavior?

NestJS

import * as Joi from 'joi';

const schema = Joi.object({
  username: Joi.string().min(3).required(),
  age: Joi.number().integer().min(18).required()
});

// Assume this schema is used in a validation pipe in a controller method

A The controller method runs normally but with undefined or default values for invalid fields.

B The invalid fields are automatically corrected to default valid values and the method runs.

C The request is rejected and a 400 Bad Request error is sent with validation error details.

D The server crashes with an unhandled exception due to Joi validation failure.

💡 Hint

Think about how NestJS validation pipes handle schema validation failures.

When Joi validation fails in a NestJS validation pipe, the framework automatically responds with a 400 Bad Request error and includes details about which fields failed validation.

📝 Syntax

intermediate

Which Joi schema correctly validates an object with an optional email and a required password of at least 8 characters?

Choose the Joi schema that correctly matches the requirements:

• email: optional, must be a valid email if present
• password: required, string, minimum length 8

A Joi.object({ email: Joi.string().email().required(), password: Joi.string().min(8) })

B Joi.object({ email: Joi.string().email(), password: Joi.string().min(8).required() })

C Joi.object({ email: Joi.string().optional(), password: Joi.string().min(8).required() })

D Joi.object({ email: Joi.email().optional(), password: Joi.string().min(8).required() })

💡 Hint

Remember that by default fields are optional unless marked required.

Option B correctly sets email as optional (default) and password as required with minimum length 8. Option B requires email and password is optional. Option B is valid but redundant because Joi.string() is optional by default. Option B uses Joi.email() which is invalid syntax.

🔧 Debug

advanced

Why does this Joi validation schema cause a runtime error?

Examine the following Joi schema and identify the cause of the runtime error:

NestJS

const schema = Joi.object({
  name: Joi.string().min(3),
  age: Joi.number().integer().min(0),
  email: Joi.string().email().required(),
});

A The schema object must be wrapped in Joi.object().keys() instead of Joi.object().

B The min(3) on name is invalid because min only works on numbers.

C Joi.number().integer() is invalid syntax and causes the error.

D The .required method is missing parentheses, so email is not marked required correctly.

💡 Hint

Check the syntax of method calls on Joi validators.

The .required method must be called with parentheses as .required(). Without parentheses, it is a reference to the function, not a call, causing the schema to be invalid and throwing a runtime error.

❓ state_output

advanced

What is the output of this Joi validation result?

Given the schema and input below, what is the value of result.error after validation?

NestJS

const schema = Joi.object({
  username: Joi.string().alphanum().min(3).max(10).required(),
  password: Joi.string().pattern(new RegExp('^[a-zA-Z0-9]{3,30}$')).required()
});

const input = { username: 'ab', password: '123' };

const result = schema.validate(input);

A An error object indicating username is too short

B An error object indicating both username and password are invalid

C An error object indicating password pattern mismatch

D null (no error, validation passed)

💡 Hint

Check the username length and password pattern against the input.

The username 'ab' is only 2 characters, which is less than the minimum 3, so validation fails with an error about username length. The password '123' matches the pattern, so no error there.

🧠 Conceptual

expert

How does Joi validation integrate with NestJS pipes for request validation?

Which statement best describes how Joi schemas are used within NestJS validation pipes to validate incoming requests?

A Joi schemas are passed to a custom validation pipe that runs validation and throws exceptions on failure, integrating with NestJS exception filters.

B NestJS automatically converts Joi schemas to class-validator decorators without extra code.

C Joi validation is only used on the client side and does not integrate with NestJS pipes.

D NestJS uses Joi schemas internally by default without needing to define validation pipes.

💡 Hint

Think about how validation pipes work and how Joi can be used in them.

Joi schemas are used in custom validation pipes in NestJS. The pipe runs Joi validation on the incoming data and throws exceptions if validation fails. This integrates with NestJS's exception handling system to send proper error responses.