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validation pipes in nestjs are a powerful feature that helps ensure the integrity of data coming into your application. they automatically validate incoming requests based on the dtos (data transfer objects) defined in your application, making it easier to enforce rules and constraints.

what are validation pipes?

validation pipes are used to validate and transform incoming request data. they can check if the data matches the expected format, ensure required fields are present, and even transform data types (e.g., converting strings to numbers).

setting up a nestjs project

first, make sure you have a nestjs project set up. if you don’t have one, you can create a new project using the nest cli:

```bash
npm i -g @nestjs/cli
nest new validation-example
cd validation-example
```

installing required packages

to use validation pipes, you'll need to install the `class-validator` and `class-transformer` packages:

```bash
npm install class-validator class-transformer
```

creating a dto

a dto is a simple class that defines the structure of the data you expect. you can use decorators provided by `class-validator` to define validation rules. for example, let’s create a dto for a user registration:

```typescript
// src/users/dto/create-user.dto.ts

import { isstring, isemail, isnotempty, isint, min, max } from 'class-validator';

export class createuserdto {
@isstring()
@isnotempty()
username: string;

@isemail()
@isnotempty()
email: string;

@isstring()
@isnotempty()
password: string;

@isint()
@min(1)
@max(120)
age: number;
}
```

using validation pipes

you can apply the validation pipe globally or at the route handler level.

1. global validation pipe

to apply a validation pipe globally, you can do this in the main application file (`main.ts`):

```typescript
// src/main.ts

import { nestfactory } from '@nestjs/core';
import { appmodule } from './app.module';
import { validationpipe } from '@nestjs/common';

async function bootstrap ...

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