# UploadedFile

**Kind:** Function

**Source:** [`packages/common/decorators/http/route-params.decorator.ts`](https://github.com/nestjs/nest/blob/master/packages/common/decorators/http/route-params.decorator.ts#L241)

**Part of:** [Common](subsystem-packages-common)

Route handler parameter decorator. Extracts the `file` object
and populates the decorated parameter with the value of `file`.
Used in conjunction with
[multer middleware](https://github.com/expressjs/multer) for Express-based applications.

For example:
```typescript
uploadFile(@UploadedFile() file) {
  console.log(file);
}
```

`@UploadedFile()` is a route handler parameter decorator that reads the uploaded file object from the request and assigns it to the decorated parameter. In Express applications, it works with Multer middleware or a Nest file interceptor that places a file on the request.

## Signature

```ts
function UploadedFile(fileKey: string | (Type<PipeTransform> | PipeTransform), pipes: (Type<PipeTransform> | PipeTransform)[]): ParameterDecorator
```

## Parameters

| Name | Type |
|---|---|
| `fileKey` | `string | (Type<PipeTransform> | PipeTransform)` |
| `pipes` | `(Type<PipeTransform> | PipeTransform)[]` |

**Returns:** `ParameterDecorator`

## Diagram

```mermaid
graph LR
  Client[Client multipart request] --> Middleware[Multer or FileInterceptor]
  Middleware --> Request[Request with file object]
  Request --> Decorator[@UploadedFile()]
  Decorator --> Handler[Route handler parameter]
```

## Usage

```typescript
import {
  Controller,
  Post,
  UploadedFile,
  UseInterceptors,
} from '@nestjs/common';
import { FileInterceptor } from '@nestjs/platform-express';

@Controller('uploads')
export class UploadController {
  @Post()
  @UseInterceptors(FileInterceptor('file'))
  uploadFile(@UploadedFile() file: Express.Multer.File) {
    return {
      filename: file.filename,
      mimetype: file.mimetype,
      size: file.size,
    };
  }
}
```

## AI Coding Instructions

- Pair `@UploadedFile()` with Multer middleware or `FileInterceptor()` so the request contains a file object.
- Match the field name passed to `FileInterceptor('file')` with the multipart form field sent by the client.
- Handle missing files when the upload field is optional or middleware may reject the request.
- Add validation pipes or file checks when routes need to restrict file type or size.