CRUD operations in NestJS

Introduction

CRUD operations let you create, read, update, and delete data in your app. They are the basic actions to manage information.

Building a user management system where you add, view, edit, or remove users.

Creating a blog where you write, read, update, or delete posts.

Managing products in an online store with add, list, update, and delete features.

Syntax

NestJS

import { Controller, Get, Post, Put, Delete, Body, Param } from '@nestjs/common';

@Controller('items')
export class ItemsController {
  @Get()
  findAll() {}

  @Get(':id')
  findOne(@Param('id') id: string) {}

  @Post()
  create(@Body() createItemDto) {}

  @Put(':id')
  update(@Param('id') id: string, @Body() updateItemDto) {}

  @Delete(':id')
  remove(@Param('id') id: string) {}
}

Use decorators like @Get, @Post, @Put, and @Delete to define HTTP methods.

@Param gets data from the URL, @Body gets data from the request body.

Examples

Gets all items when you visit /items with a GET request.

NestJS

@Get()
findAll() {
  return 'Return all items';
}

Creates a new item using data sent in the request body.

NestJS

@Post()
create(@Body() createItemDto) {
  return `Create item with name: ${createItemDto.name}`;
}

Updates an existing item by its ID with new data.

NestJS

@Put(':id')
update(@Param('id') id: string, @Body() updateItemDto) {
  return `Update item ${id} with name: ${updateItemDto.name}`;
}

Deletes an item by its ID.

NestJS

@Delete(':id')
remove(@Param('id') id: string) {
  return `Delete item with id ${id}`;
}

Sample Program

This controller manages a list of items in memory. You can add, get, update, and delete items by their ID.

NestJS

import { Controller, Get, Post, Put, Delete, Body, Param } from '@nestjs/common';

interface Item {
  id: number;
  name: string;
}

@Controller('items')
export class ItemsController {
  private items: Item[] = [];
  private idCounter = 1;

  @Get()
  findAll(): Item[] {
    return this.items;
  }

  @Get(':id')
  findOne(@Param('id') id: string): Item | string {
    const item = this.items.find(i => i.id === +id);
    return item || 'Item not found';
  }

  @Post()
  create(@Body() createItemDto: { name: string }): Item {
    const newItem = { id: this.idCounter++, name: createItemDto.name };
    this.items.push(newItem);
    return newItem;
  }

  @Put(':id')
  update(@Param('id') id: string, @Body() updateItemDto: { name: string }): Item | string {
    const item = this.items.find(i => i.id === +id);
    if (!item) return 'Item not found';
    item.name = updateItemDto.name;
    return item;
  }

  @Delete(':id')
  remove(@Param('id') id: string): string {
    const index = this.items.findIndex(i => i.id === +id);
    if (index === -1) return 'Item not found';
    this.items.splice(index, 1);
    return `Deleted item with id ${id}`;
  }
}

Important Notes

In real apps, data usually comes from a database, not memory.

Use DTOs (Data Transfer Objects) to validate and type-check data.

Each HTTP method matches a CRUD action: GET=read, POST=create, PUT=update, DELETE=delete.

Summary

CRUD operations let you manage data by creating, reading, updating, and deleting.

In NestJS, use controllers with decorators like @Get, @Post, @Put, and @Delete.

Use @Param to get URL data and @Body to get data sent by the client.

Practice

1. In NestJS, which decorator is used in a controller method to handle HTTP POST requests for creating data?

easy

A. @Post

B. @Get

C. @Put

D. @Delete

Solution

1. Step 1: Understand HTTP methods and their NestJS decorators

   HTTP POST is used to create new data. NestJS uses @Post decorator for this.

2. Step 2: Match the decorator to the HTTP method

   @Get is for reading, @Put for updating, and @Delete for deleting data, so they don't fit creating data.

3. Final Answer:

   @Post -> Option A

4. Quick Check:

   POST = @Post [OK]

Hint: POST requests use @Post decorator in NestJS controllers [OK]

Common Mistakes:

• Confusing @Get with @Post
• Using @Put for creating data
• Using @Delete for creation

2. Which of the following is the correct way to extract a route parameter named id in a NestJS controller method?

easy

A. async getItem(@Body('id') id: string) {}

B. async getItem(@Query('id') id: string) {}

C. async getItem(@Param('id') id: string) {}

D. async getItem(@Headers('id') id: string) {}

Solution

1. Step 1: Identify the decorator for route parameters

   @Param is used to extract parameters from the URL path, such as /items/:id.

2. Step 2: Check other decorators and their uses

   @Body extracts data from the request body, @Query from query strings, and @Headers from HTTP headers, so they don't get route params.

3. Final Answer:

   async getItem(@Param('id') id: string) {} -> Option C

4. Quick Check:

   Route param = @Param [OK]

Hint: Use @Param to get URL parameters in NestJS [OK]

Common Mistakes:

• Using @Body to get URL params
• Using @Query for route params
• Confusing @Headers with @Param

3. Given this NestJS controller method, what will be the response if a client sends a DELETE request to /items/5 and the service deletes the item successfully?

  @Delete(':id')
  async remove(@Param('id') id: string) {
    await this.itemsService.delete(id);
    return { message: `Item ${id} deleted` };
  }

medium

A. HTTP 404 Not Found

B. { "message": "Item 5 deleted" }

C. { "error": "Item not found" }

D. Empty response with HTTP 204 No Content

Solution

1. Step 1: Analyze the controller method's return value

   The method returns an object with a message string including the id parameter.

2. Step 2: Understand the response for successful deletion

   Since the method returns a JSON object with the message, the client receives that JSON with HTTP 200 OK by default.

3. Final Answer:

   { "message": "Item 5 deleted" } -> Option B

4. Quick Check:

   Return JSON message on success = { "message": "Item 5 deleted" } [OK]

Hint: Returned object becomes JSON response by default in NestJS [OK]

Common Mistakes:

• Expecting HTTP 204 No Content without explicit status
• Assuming error response without checking service
• Confusing DELETE with GET response

4. Identify the error in this NestJS controller method for updating an item:

  @Put(':id')
  async update(@Body() updateDto: UpdateItemDto) {
    return this.itemsService.update(updateDto.id, updateDto);
  }

medium

A. Method should be named create, not update

B. Using @Body instead of @Query for update data

C. UpdateItemDto cannot be used in @Body

D. Missing @Param decorator to get the id from URL

Solution

1. Step 1: Check how the id is obtained

   The method expects id from updateDto.id, but the route has ':id' parameter which is not extracted.

2. Step 2: Identify missing @Param decorator

   To get id from URL, @Param('id') id: string should be added as a parameter to the method.

3. Final Answer:

   Missing @Param decorator to get the id from URL -> Option D

4. Quick Check:

   URL param needs @Param [OK]

Hint: Use @Param to get URL id in update methods [OK]

Common Mistakes:

• Assuming id comes from body without @Param
• Confusing @Body with @Query
• Ignoring route parameters

5. You want to implement a NestJS controller method to update an item by its id from the URL and new data from the request body. Which of the following method signatures correctly follows NestJS CRUD patterns?

hard

A. async update(@Param('id') id: string, @Body() updateDto: UpdateItemDto) { return this.itemsService.update(id, updateDto); }

B. async update(@Body('id') id: string, @Body() updateDto: UpdateItemDto) { return this.itemsService.update(id, updateDto); }

C. async update(@Query('id') id: string, @Body() updateDto: UpdateItemDto) { return this.itemsService.update(id, updateDto); }

D. async update(@Param() params: any) { return this.itemsService.update(params.id, params); }

Solution

1. Step 1: Identify correct decorators for id and body

   Use @Param('id') to get id from URL and @Body() to get update data object.

2. Step 2: Check method parameters and service call

   async update(@Param('id') id: string, @Body() updateDto: UpdateItemDto) { return this.itemsService.update(id, updateDto); } correctly separates id and updateDto and calls service with both.

3. Final Answer:

   async update(@Param('id') id: string, @Body() updateDto: UpdateItemDto) { return this.itemsService.update(id, updateDto); } -> Option A

4. Quick Check:

   Use @Param for id, @Body for data [OK]

Hint: Use @Param('id') and @Body() together for update methods [OK]

Common Mistakes:

• Using @Body('id') instead of @Param('id')
• Using @Query for route params
• Passing params object instead of separate arguments