# Patch

**Kind:** Constant

**Source:** [`packages/common/decorators/http/request-mapping.decorator.ts`](https://github.com/nestjs/nest/blob/master/packages/common/decorators/http/request-mapping.decorator.ts#L84)

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

Route handler (method) Decorator. Routes HTTP PATCH requests to the specified path.

`Patch` is a method decorator that maps an HTTP `PATCH` request to a controller handler. It is used to define endpoints for partial resource updates and delegates route metadata creation to the shared request-mapping decorator infrastructure.

## Definition

```ts
createMappingDecorator(RequestMethod.PATCH)
```

## Value

```ts
createMappingDecorator(RequestMethod.PATCH)
```

## Diagram

```mermaid
graph LR
  Client[HTTP Client] -->|PATCH /resource/:id| Router[Nest Router]
  Router --> Controller[Controller Method]
  Patch["@Patch(path) decorator"] -->|Registers PATCH route metadata| Controller
  Controller --> Handler[Update Resource Logic]
```

## Usage

```ts
import { Body, Controller, Param, Patch } from '@nestjs/common';

@Controller('users')
export class UsersController {
  @Patch(':id')
  updateUser(
    @Param('id') id: string,
    @Body() updateUserDto: { displayName?: string },
  ) {
    return {
      id,
      ...updateUserDto,
    };
  }
}
```

## AI Coding Instructions

- Apply `@Patch()` only to controller methods that handle partial updates of an existing resource.
- Provide a path such as `':id'` when the handler needs to identify a specific resource.
- Use DTOs with optional fields for PATCH request bodies rather than requiring a complete resource payload.
- Combine `@Patch()` with parameter decorators such as `@Param()`, `@Body()`, and validation pipes as needed.
- Avoid using `@Patch()` for full replacement semantics; prefer `@Put()` when clients must send the complete resource representation.

## Used by

4 references from 4 files. Each is a place in this repository where the symbol is actually used — go read one rather than trusting an example.

### Imported by (4)

- `DatabaseController` — `integration/inspector/src/database/database.controller.ts`:14
- `DogsController` — `integration/inspector/src/dogs/dogs.controller.ts`:14
- `UsersController` — `integration/inspector/src/users/users.controller.ts`:14
- `UsersController` — `integration/repl/src/users/users.controller.ts`:14