Set Up GET Queries - Get All and Get By ID

Introduction and Context Setting

Welcome to the first lesson of our course on "Building a To-Do REST API with NestJS" . In this course, we'll learn how to create a To-Do application using NestJS . A REST API (Representational State Transfer Application Programming Interface) is a way for different software systems to communicate over the internet. NestJS is a framework for building efficient, reliable, and scalable server-side applications with REST at the core. NestJS provides built-in support for complete application development, making it a versatile choice for building APIs. It is built on top of Express.js but adds many valuable features and an Angular-inspired structure to make development easier.

Setting Up the Project Environment

Before we dive into the code, let's set up our project environment. Although the CodeSignal environment comes pre-installed with necessary libraries, it's essential to know how to set things up locally. Installing NestJS Locally : First, you need Node.js installed on your system. You can download it from Node.js . Install the Nest CLI globally using npm : Shell npm install -g @nestjs/cli npm install -g @nestjs/cli Create a new project using the Nest CLI: Shell nest new todo-app nest new todo-app Project Structure : The basic file structure includes: src/ folder: Contains the main application files. main.ts : The entry file for the application. app.module.ts : The root module of the application. For our example, we'll assume the environment is already set up on CodeSignal.

Creating the TodoController

Controllers in NestJS handle incoming requests and return responses to the client. Let's create our TodoController . In a REST API, you will want to map web requets with different verbs. The most common verb is GET which indicates that you are querying data, not modifying it. It is very common in a REST API to include two GET handlers for a Resource. In this case, our Resource is Todo and our GET queries handle getting all Todo s in addition to getting a single Todo by ID.

Step-by-Step Code

TypeScript import { Controller, Get, Param } from '@nestjs/common'; import { TodoService } from './todo.service'; import { TodoDto } from './dto/todo.dto'; @Controller('todos') // Define the controller to handle all /todos routes export class TodoController {constructor(private readonly todoService: TodoService) {} // Inject the TodoServices @Get() // Handle the GET request for getting all Todos via /todos findAll(): TodoDto[] {return this.todoService.findAll();} @Get(':id') // Extend the /todos route to GET a single Todo via the /todos/:id route findOne(// Use the @Param('id') decorator to decoare that the :id in the route will map to the id parameter @Param('id') id: string,): TodoDto {return this.todoService.findOne(id);}} import { Controller, Get, Param } from '@nestjs/common'; import { TodoService } from './todo.service'; import { TodoDto } from './dto/todo.dto'; @Controller('todos') // Define the controller to handle all /todos routes export class TodoController {constructor(private readonly todoService: TodoService) {} // Inject the TodoServices @Get() // Handle the GET request for getting all Todos via /todos findAll(): TodoDto[] {return this.todoService.findAll();} @Get(':id') // Extend the /todos route to GET a single Todo via the /todos/:id route findOne(// Use the @Param('id') decorator to decoare that the :id in the route will map to the id parameter @Param('id') id: string,): TodoDto {return this.todoService.findOne(id);}}

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Shell

npm install -g @nestjs/cli

Shell

nest new todo-app

TypeScript

import { Controller, Get, Param } from '@nestjs/common';
import { TodoService } from './todo.service';
import { TodoDto } from './dto/todo.dto';

@Controller('todos') // Define the controller to handle all /todos routes
export class TodoController {
  constructor(private readonly todoService: TodoService) {} // Inject the TodoServices

  @Get() // Handle the GET request for getting all Todos via /todos
  findAll(): TodoDto[] {
    return this.todoService.findAll();
  }

  @Get(':id') // Extend the /todos route to GET a single Todo via the /todos/:id route
  findOne(
    // Use the @Param('id') decorator to decoare that the :id in the route will map to the id parameter
    @Param('id') id: string,
  ): TodoDto {
    return this.todoService.findOne(id);
  }
}

TypeScript

import { Injectable } from '@nestjs/common';
import { TodoDto } from './dto/todo.dto';

@Injectable() // Declare the TodoService to be available as an injectable service via Dependency Injection
export class TodoService {
    
  // For now, let's populate this service with some data
  private todos: TodoDto[] = [
    {
      id: '1',
      title: 'Learn NestJS',
      description: 'Learn how to build with NestJS',
      completed: true,
    },
    {
      id: '2',
      title: 'Learn REST',
      description: 'Learn how to build interactive REST APIs',
      completed: false,
    },
  ];

  // fetch all of the Todo items. 
  findAll(showIncomplete?: boolean): TodoDto[] {
    return this.todos;
  }

  // fetch only one item and return null if it does not exist.
  findOne(id: string): TodoDto | null {
    return this.todos.find(todo => todo.id === id) || null;
  }
}

import { Injectable } from '@nestjs/common';
import { TodoDto } from './dto/todo.dto';

@Injectable() // Declare the TodoService to be available as an injectable service via Dependency Injection
export class TodoService {
    
  // For now, let's populate this service with some data
  private todos: TodoDto[] = [
    {
      id: '1',
      title: 'Learn NestJS',
      description: 'Learn how to build with NestJS',
      completed: true,
    },
    {
      id: '2',
      title: 'Learn REST',
      description: 'Learn how to build interactive REST APIs',
      completed: false,
    },
  ];

  // fetch all of the Todo items. 
  findAll(showIncomplete?: boolean): TodoDto[] {
    return this.todos;
  }

  // fetch only one item and return null if it does not exist.
  findOne(id: string): TodoDto | null {
    return this.todos.find(todo => todo.id === id) || null;
  }
}

TypeScript

import { Injectable } from '@nestjs/common';
import { TodoDto } from './dto/todo.dto';

@Injectable() // Declare the TodoService to be available as an injectable service via Dependency Injection
export class TodoService {
    
  // For now, let's populate this service with some data
  private todos: TodoDto[] = [
    {
      id: '1',
      title: 'Learn NestJS',
      description: 'Learn how to build with NestJS',
      completed: true,
    },
    {
      id: '2',
      title: 'Learn REST',
      description: 'Learn how to build interactive REST APIs',
      completed: false,
    },
  ];

  // fetch all of the Todo items. 
  findAll(showIncomplete?: boolean): TodoDto[] {
    return this.todos;
  }

  // fetch only one item and return null if it does not exist.
  findOne(id: string): TodoDto | null {
    return this.todos.find(todo => todo.id === id) || null;
  }
}

Introduction and Context Setting

Setting Up the Project Environment

Creating the TodoController

Step-by-Step Code

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Creating the TodoService

Step-by-Step Code

Connecting the Controller and Service

Step-by-Step Explanation

Summary and Next Steps