Validation with Joi in NestJS - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to import Joi for validation.

NestJS

import * as [1] from 'joi';

Drag options to blanks, or click blank then click option'

Aexpress

BJoi

Cnestjs

Dclass-validator

Attempts:

3 left

💡 Hint

Common Mistakes

Importing from 'express' or 'nestjs' instead of 'joi'.

Using 'class-validator' which is a different validation library.

Joi is imported as a namespace to use its validation functions.

2fill in blank

medium

Complete the code to define a Joi schema for a username that is a required string.

NestJS

const schema = Joi.object({ username: Joi.[1]().required() });

Drag options to blanks, or click blank then click option'

Anumber

Barray

Cboolean

Dstring

Attempts:

3 left

💡 Hint

Common Mistakes

Using number() or boolean() instead of string().

Forgetting to call required() to make the field mandatory.

The username should be a string, so we use Joi.string().

3fill in blank

hard

Fix the error in the validation pipe setup by completing the missing property.

NestJS

app.useGlobalPipes(new ValidationPipe({ whitelist: [1] }));

Drag options to blanks, or click blank then click option'

Afalse

Bnull

Ctrue

Dundefined

Attempts:

3 left

💡 Hint

Common Mistakes

Setting whitelist to false or null disables property filtering.

Leaving whitelist undefined means no filtering happens.

Setting whitelist: true removes properties not in the DTO.

4fill in blank

hard

Fill both blanks to create a Joi schema for an email that is required and must be valid.

NestJS

const schema = Joi.object({ email: Joi.[1]().[2]() });

Drag options to blanks, or click blank then click option'

Astring

Bemail

Crequired

Dvalid

Attempts:

3 left

💡 Hint

Common Mistakes

Using email() instead of string() (email is a validator, not a type).

Forgetting to add required().

Email should be a string and required, so use string() and required().

5fill in blank

hard

Fill all three blanks to create a Joi schema for a password that is a required string with minimum length 8.

NestJS

const schema = Joi.object({ password: Joi.[1]().min([2]).[3]() });

Drag options to blanks, or click blank then click option'

Astring

B8

Crequired

Dnumber

Attempts:

3 left

💡 Hint

Common Mistakes

Using number() instead of string().

Forgetting to call required().

Setting min to a string instead of a number.

Password must be a string, at least 8 characters, and required.

Practice

1. What is the main purpose of using Joi in a NestJS application?

easy

A. To style the user interface

B. To manage database connections

C. To handle HTTP routing

D. To validate and enforce rules on incoming data

Solution

1. Step 1: Understand Joi's role

   Joi is a library used to define schemas that describe how data should look and to check if data matches those rules.

2. Step 2: Identify the correct purpose in NestJS

   In NestJS, Joi is used to validate incoming data to ensure it meets expected formats and constraints before processing.

3. Final Answer:

   To validate and enforce rules on incoming data -> Option D

4. Quick Check:

   Joi = Data validation [OK]

Hint: Joi is for checking data shapes and rules [OK]

Common Mistakes:

• Confusing Joi with database or routing tools
• Thinking Joi styles UI elements
• Assuming Joi manages server configuration

2. Which of the following is the correct way to define a Joi schema for a required string field named username?

easy

A. Joi.string().required()

B. Joi.number().required()

C. Joi.boolean().optional()

D. Joi.array().required()

Solution

1. Step 1: Identify the data type for username

   A username is typically a string, so the schema should start with Joi.string().

2. Step 2: Make the field required

   Adding .required() ensures the field must be present and not empty.

3. Final Answer:

   Joi.string().required() -> Option A

4. Quick Check:

   String + required = Joi.string().required() [OK]

Hint: Use Joi.string().required() for mandatory text fields [OK]

Common Mistakes:

• Using wrong Joi types like number or boolean for strings
• Forgetting to add .required() for mandatory fields
• Confusing optional() with required()

3. Given this Joi schema:

const schema = Joi.object({ age: Joi.number().min(18).required() });
const result = schema.validate({ age: 16 });

What will result.error contain?

medium

A. No error, validation passes

B. An error indicating age must be at least 18

C. An error indicating age is missing

D. An error indicating age must be a string

Solution

1. Step 1: Analyze the schema rules

   The schema requires age to be a number, at least 18, and required.

2. Step 2: Check the input data

   The input has age: 16, which is less than the minimum 18.

3. Step 3: Determine validation result

   Validation fails because 16 is below the minimum, so result.error contains a message about age being too low.

4. Final Answer:

   An error indicating age must be at least 18 -> Option B

5. Quick Check:

   Age 16 < 18 = validation error [OK]

Hint: Check min() rules against input values [OK]

Common Mistakes:

• Assuming 16 passes min(18) validation
• Confusing missing field error with min value error
• Expecting string type error instead of number

4. Identify the error in this Joi schema definition:

const schema = Joi.object({
  email: Joi.string().email,
  password: Joi.string().min(8).required()
});

medium

A. email should be Joi.email() instead of Joi.string().email

B. password should not be required

C. Missing parentheses after email() method

D. min(8) is invalid for strings

Solution

1. Step 1: Review the email field syntax

   The email method in Joi is a function and must be called with parentheses: email().

2. Step 2: Identify the missing parentheses

   The code uses Joi.string().email without parentheses, which is incorrect and will cause an error.

3. Final Answer:

   Missing parentheses after email() method -> Option C

4. Quick Check:

   Joi methods require () to execute [OK]

Hint: Always add () after Joi methods like email() [OK]

Common Mistakes:

• Omitting parentheses on Joi method calls
• Misunderstanding required() necessity
• Thinking min() is invalid for strings

5. You want to validate a user object with name (required string), age (optional number, minimum 0), and email (required valid email). Which Joi schema correctly applies these rules?

hard

A. Joi.object({ name: Joi.string().required(), age: Joi.number().min(0), email: Joi.string().email().required() })

B. Joi.object({ name: Joi.string(), age: Joi.number().min(0).required(), email: Joi.string().email() })

C. Joi.object({ name: Joi.string().required(), age: Joi.number().min(1).optional(), email: Joi.string().email().required() })

D. Joi.object({ name: Joi.string().required(), age: Joi.number().min(0).required(), email: Joi.string().email().required() })

Solution

1. Step 1: Check each field's requirements

   Name must be a required string, age is optional number with min 0, email is required valid email string.

2. Step 2: Match schema to requirements

   Joi.object({ name: Joi.string().required(), age: Joi.number().min(0), email: Joi.string().email().required() }) matches all: name is required string, age is number with min 0 (optional by default), email is required email string.

3. Step 3: Verify other options

   Joi.object({ name: Joi.string(), age: Joi.number().min(0).required(), email: Joi.string().email() }) makes age required and email optional, Joi.object({ name: Joi.string().required(), age: Joi.number().min(1).optional(), email: Joi.string().email().required() }) uses min(1) for age (wrong min), Joi.object({ name: Joi.string().required(), age: Joi.number().min(0).required(), email: Joi.string().email().required() }) makes age required (wrong).

4. Final Answer:

   Joi.object({ name: Joi.string().required(), age: Joi.number().min(0), email: Joi.string().email().required() }) -> Option A

5. Quick Check:

   Required fields + optional age min 0 = Joi.object({ name: Joi.string().required(), age: Joi.number().min(0), email: Joi.string().email().required() }) [OK]

Hint: Required fields use .required(), optional omit it [OK]

Common Mistakes:

• Making optional fields required by mistake
• Using wrong min values for age
• Forgetting to call email() with parentheses