[Nest.js] 6 - DTO & PIPES

Contents
1. DTO? Mapped-Type?
2. Pipes?
3. Binding Pipes
4. Built-in 8 Pipes
5. Custom Pipe

---

1. DTO?

- Data Transfer Object

- Mostly, to use in Controllers to validate request objects(e.g., data inputs from client)

- When Client requests and receives data with Server, we need regulations for data type, name, and so on.
  -> Nest supports that those data automatically convert to class, which is called by DTO

 

Example

- Create "dto" folder

 

- Create "create-board.dto.ts" to use in POST request from client

// boards/dto/create-board.dto.ts

export class CreateBoardDto {
  title: string;
  description: string;
}

 - Use in Controller

// boards/boards.controller.ts

@Post()
createBoard(@Body() createBoardDto: CreateBoardDto): Promise<Board> {
  return this.boardsService.createBoard(createBoardDto);
}

 

Mapped-Type?

- install mapped-type module

$ npm i @nestjs/mapped-types

 

- Nest supports to create DTOs easily by using gql schema and entity.

- Mapped Type : Partial, Pick, Omit, Intersection

 

1. Partial

- In many cases for input validation types, "Create" and "Update" arguments are almost the same.
   -> Create : required
   -> Update : optional

- using create dto

- making update dto, which consist of optional properties, title and description

.

- will update other types later ... 

---

2. Pipes?

- A Pipe is a class with @Injectable() decorator, and Implements the "PipeTransform" interface

https://docs.nestjs.com/pipes

- Pipes work for Route Handlers' parameters

 

Data Transformation

- transfer input data to what we need to be(e.g., string to number)

- if we need a number type parameter from client, Pipe converts its type to number.

Data Validation

- validate input data whether it is correct type in Dto, or arguments.

- if we need a name property in length 10, and client sent more than length 10 value, it causes an error.

---

3. Binding Pipes

 

1. Global-level Pipes( = application-level Pipe)

- apply all requests from client

- app.useGlobalPipes(PipeClass)

All Request

 

2. Handler-level Pipes

- apply where a request corresponding to Handler

- @UsePipe(pipeClass) decorator in Handler-level

createBoard

 

3. Parameter-level Pipes

- appply on a specific parameter in Handler

title parameter

---

4. Built-in Pipes

 

1. ValidationPipe

- @IsNotEmpty() decorator in dto class

 

boards/dto/create-board.dto.ts

 

- @UsePipes(ValidationPipe) decorator in Handler-Level

boards/boards.controller.ts

- POST request without any input data

 

- 400 error response, and show up what needed to  

400 error response

 

2. ParseIntPipe

- @Param('id', ParseIntPipe) in Parameter-Level Pipe

- GET request with unable parsing data, alphabets

Request data in string type

- 400 error response, and show up which validation failed

400 error response 

3. ParseFloatPipe

4. ParseBoolPipe

5. ParseArrayPipe

6. ParseUUIDPipe

7. ParseEnumPipe

8. DefaultValuePipe

---

5. custom Pipes

- implements "PipeTransform" interface

- transform() method 
   - it has two parameter, and return statement, which sends to Route Handler

- if it occurs an error, it goes to Client with error response directly.
 

Example

- create a Custom Pipe 

boards/pipes/board-status-validation.pipe.ts

- set the pipe in Handler, parameter-level

boards/boards.controller.ts