Default value pipe in NestJS - Mini Project: Build & Apply

Using Default Value Pipe in NestJS

📖 Scenario: You are building a simple NestJS controller to handle user queries. Sometimes users may not provide a query parameter, so you want to set a default value automatically.

🎯 Goal: Create a NestJS controller with a GET endpoint that uses the DefaultValuePipe to provide a default value for a query parameter called page.

📋 What You'll Learn

Create a controller class named AppController.

Add a GET route handler method named getItems.

Use the @Query decorator with DefaultValuePipe to set a default value of 1 for the page query parameter.

Return the page value as a number from the handler.

💡 Why This Matters

🌍 Real World

Setting default values for query parameters is common in APIs to handle missing inputs gracefully.

💼 Career

Understanding pipes like DefaultValuePipe is essential for building robust and user-friendly APIs in NestJS.

1

Create the controller class and import necessary decorators

Create a class called AppController and import Controller and Get from @nestjs/common.

NestJS

import { Controller, Get } from '@nestjs/common';

// Your code here

Need a hint?

Use export class AppController and decorate it with @Controller().

2

Add the GET route handler method

Inside AppController, add a method named getItems decorated with @Get() that returns 0 for now.

NestJS

import { Controller, Get } from '@nestjs/common';

@Controller()
export class AppController {
  // Your code here
}

Need a hint?

Define getItems() method and decorate it with @Get().

3

Import and use DefaultValuePipe for the query parameter

Import Query and DefaultValuePipe from @nestjs/common. Modify getItems to accept a page parameter from query using @Query('page', new DefaultValuePipe('1')).

NestJS

import { Controller, Get, Query, DefaultValuePipe } from '@nestjs/common';

@Controller()
export class AppController {
  @Get()
  getItems(
    // Your code here
  ) {
    return 0;
  }
}

Need a hint?

Use @Query('page', new DefaultValuePipe('1')) to set default page value.

4

Convert the page parameter to a number before returning

Modify the getItems method to convert the page parameter from string to number using Number(page) and return it.

NestJS

import { Controller, Get, Query, DefaultValuePipe } from '@nestjs/common';

@Controller()
export class AppController {
  @Get()
  getItems(
    @Query('page', new DefaultValuePipe('1')) page: string
  ) {
    // Your code here
  }
}

Need a hint?

Use Number(page) to convert the string to a number before returning.