CRUD operations in NestJS - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does CRUD stand for in software development?

CRUD stands for Create, Read, Update, and Delete. These are the four basic operations to manage data in applications.

beginner

In NestJS, which decorator is commonly used to define a method that handles HTTP POST requests for creating data?

The @Post() decorator is used in NestJS controllers to define a method that handles HTTP POST requests, typically for creating new data.

intermediate

How does NestJS help organize CRUD operations in an application?

NestJS organizes CRUD operations using controllers for routing HTTP requests and services for business logic, keeping code clean and modular.

beginner

What HTTP method and NestJS decorator pair is used to update existing data?

The HTTP PUT or PATCH method is used to update data. In NestJS, @Put() or @Patch() decorators define methods handling these requests.

intermediate

Why is it important to separate controller and service logic in NestJS when implementing CRUD?

Separating controller and service logic improves code clarity, makes testing easier, and allows reusing business logic across different parts of the app.

Which NestJS decorator is used to handle HTTP GET requests for reading data?

A @Post()

B @Delete()

C @Put()

D @Get()

The @Get() decorator is used to define methods that handle HTTP GET requests, which are typically used to read or retrieve data.

What HTTP method is typically used to delete data in a RESTful API?

A POST

B GET

C DELETE

D PUT

The DELETE HTTP method is used to remove data from the server.

In NestJS, where should the main business logic for CRUD operations be placed?

A In the service

B In the controller

C In the module

D In the main.ts file

Business logic should be placed in services to keep controllers focused on handling requests and responses.

Which HTTP method and NestJS decorator pair is used to create new data?

A GET and @Get()

B POST and @Post()

C PUT and @Put()

D DELETE and @Delete()

POST requests, handled by @Post() in NestJS, are used to create new data.

What is the main purpose of the @Delete() decorator in NestJS?

A To delete data

B To create data

C To update data

D To read data

The @Delete() decorator defines a method that handles HTTP DELETE requests to remove data.

Explain how CRUD operations are structured in a NestJS application.

Think about where requests are handled and where the data logic lives.

Describe the role of HTTP methods in CRUD operations and how NestJS maps them with decorators.

Match each CRUD action with its HTTP method and NestJS decorator.

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