Controllers & Routing

Table of Contents

  1. What Is a Controller?
  2. Route, Query, and Body Decorators
  3. Building the tasks Routes
  4. Trying It
  5. Beginner Pitfalls

1. What Is a Controller?

A controller is a class whose job is to receive an HTTP request and return a response. Nothing more — no business logic, no direct database access. @Controller('tasks') tells Nest that every route inside this class is prefixed with /tasks.

2. Route, Query, and Body Decorators

DecoratorMaps to
@Get()GET request
@Post()POST request
@Patch()PATCH request (partial update)
@Delete()DELETE request
@Param('id')A route parameter, e.g. /tasks/:id
@Query('done')A query string parameter, e.g. /tasks?done=true
@Body()The parsed request body

These decorators pull data straight off the HTTP request and hand it to your method as a plain argument — no manual parsing.

3. Building the tasks Routes

For now the controller calls placeholder methods on TasksService that just return hardcoded data — real logic moves into the service properly in Part 4. This part is about getting the five routes wired up and reachable.

// src/tasks/tasks.service.ts
import { Injectable } from '@nestjs/common';

@Injectable()
export class TasksService {
  findAll() {
    return [];
  }

  findOne(id: number) {
    return { id };
  }

  create(data: any) {
    return { id: Date.now(), ...data };
  }

  update(id: number, data: any) {
    return { id, ...data };
  }

  remove(id: number) {
    return { id, removed: true };
  }
}

// src/tasks/tasks.controller.ts
import {
  Body,
  Controller,
  Delete,
  Get,
  Param,
  ParseIntPipe,
  Patch,
  Post,
} from '@nestjs/common';
import { TasksService } from './tasks.service';

@Controller('tasks')
export class TasksController {
  constructor(private readonly tasksService: TasksService) {}

  @Get()
  findAll() {
    return this.tasksService.findAll();
  }

  @Get(':id')
  findOne(@Param('id', ParseIntPipe) id: number) {
    return this.tasksService.findOne(id);
  }

  @Post()
  create(@Body() body: any) {
    return this.tasksService.create(body);
  }

  @Patch(':id')
  update(@Param('id', ParseIntPipe) id: number, @Body() body: any) {
    return this.tasksService.update(id, body);
  }

  @Delete(':id')
  remove(@Param('id', ParseIntPipe) id: number) {
    return this.tasksService.remove(id);
  }
}

ParseIntPipe converts the :id route param from a string (all route params start as strings) into a number, and rejects the request with a 400 if it isn't numeric.

Note: @Body() body: any is deliberately loose for this part — real input shapes and validation arrive in Part 5.

4. Trying It

With npm run start:dev running from Part 1:

curl http://localhost:3000/tasks
curl http://localhost:3000/tasks/1
curl -X POST http://localhost:3000/tasks -H "Content-Type: application/json" -d '{"title":"Learn NestJS"}'
curl -X PATCH http://localhost:3000/tasks/1 -H "Content-Type: application/json" -d '{"title":"Learn NestJS well"}'
curl -X DELETE http://localhost:3000/tasks/1

Every route responds — with placeholder data for now.

5. Beginner Pitfalls

  • Route order matters. A literal route like @Get('search') must be declared before @Get(':id') in the same controller, or :id greedily matches search as its value.
  • Forgetting Content-Type: application/json. Without it, Nest's body parser won't parse the request body and @Body() comes back undefined.
  • Putting logic directly in the controller. It's tempting to compute the response inline here instead of delegating to the service — resist it now, before it becomes a habit. See Part 4 for why.

Official docs:

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