What is a pipe in NestJS and what are its two primary uses?

Q: What is a pipe in NestJS and what are its two primary uses?

// Transformation — ParseIntPipe converts string to number @Get(':id') findOne(@Param('id', ParseIntPipe) id: number) { // id is guaranteed to be a number // ParseIntPipe throws BadRequestException(400) if not parseable } // Validation — ValidationPipe validates the DTO @Post() create(@Body(ValidationPipe) dto: CreateUserDto) { // dto is validated against class-validator decorators // throws BadRequestException with validation errors if invalid } ParseIntPipe — converts string to integer, throws 400 if not parseable. ParseFloatPipe — converts string to float. ParseBoolPipe — converts 'true'/'false' strings to boolean. ParseUUIDPipe — validates and passes through a UUID string. ParseArrayPipe — parses comma-separated string into an array. ValidationPipe — validates DTOs using class-validator decorators. DefaultValuePipe — provides a fallback value if the input is undefined.

Difficulty: 4/10

validation, transformation, custom pipe

A pipe implements PipeTransform and operates on arguments passed to a controller handler. Its two uses are transformation (converting input to a different type, e.g. ParseIntPipe converts a string param to a number) and validation (throwing BadRequestException if input fails rules, e.g. ValidationPipe with class-validator).

Transformation pipe and validation pipe examples

Built-in pipes and their purposes:

1
ParseIntPipe — converts string to integer, throws 400 if not parseable.
2
ParseFloatPipe — converts string to float.
3
ParseBoolPipe — converts 'true'/'false' strings to boolean.
4
ParseUUIDPipe — validates and passes through a UUID string.
5
ParseArrayPipe — parses comma-separated string into an array.
6
ValidationPipe — validates DTOs using class-validator decorators.

Scenario Questions

0-2 years experience

Follow-up Questions