NestJS Pipes – Validating and Transforming Like a Pro

NestJS Pipes – Validating and Transforming Like a Pro

If you’re working with NestJS and handling user input, pipes are your best friend. They help validate and transform incoming data before it reaches your controller logic, which keeps things clean and safe.

What Exactly Are Pipes?

Pipes in NestJS operate at the route handler level and have two main roles:

1.     Validation – Ensuring the data is what you expect.

2.     Transformation – Modifying the incoming data into the right shape or type.

Think of them as a first line of defense before your business logic even sees the input.

Built-In vs Custom Pipes

Nest gives you some handy built-in pipes like ParseIntPipe, ValidationPipe, and DefaultValuePipe. For most use cases, especially with DTOs, ValidationPipe is the go-to.

But if you need something more specific—like trimming all strings, or sanitizing input—you can easily create your own custom pipes.

Quick Example: Using ValidationPipe with DTOs

Here’s how it typically looks:

ts

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import { IsString, IsInt } from ’class-validator’;

export class CreateUserDto {
  @IsString()
  name: string;

  @IsInt()
  age: number;
}



Then in your controller:

ts

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@Post()
create(@Body(new ValidationPipe()) createUserDto: CreateUserDto) {
  return this.userService.create(createUserDto);
}

Boom—your inputs are now auto-validated based on decorators. Clean and declarative.

Custom Pipe Example

Want to create a pipe that uppercases strings? Easy:

ts

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import { PipeTransform, Injectable, ArgumentMetadata } from ’@nestjs/common’;

@Injectable()
export class UppercasePipe implements PipeTransform {
  transform(value: any, metadata: ArgumentMetadata) {
    return typeof value === ’string’ ? value.toUpperCase() : value;
  }
}

Now use it like:

ts

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@Get(’:name’)
getUser(@Param(’name’, new UppercasePipe()) name: string) {
  return this.userService.findByName(name);
}

Best Practices

• Use ValidationPipe globally to cover all routes.
• Keep pipes simple and focused.
• Avoid putting heavy logic inside pipes—just validate or transform.

Pipes are one of those features that quietly make your app more robust. They enforce structure, prevent errors, and help keep your controllers clean. Once you get used to them, you’ll start wondering how you ever shipped APIs without them.