# RequestMappingMetadata

**Kind:** Interface

**Source:** [`packages/common/decorators/http/request-mapping.decorator.ts`](https://github.com/nestjs/nest/blob/master/packages/common/decorators/http/request-mapping.decorator.ts#L4)

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

`RequestMappingMetadata` describes the routing information attached to an HTTP request handler. It combines one or more URL paths with a `RequestMethod`, allowing request-mapping decorators and routing infrastructure to register controller endpoints consistently.

## Properties

| Property | Type |
|---|---|
| `path` | `string | string[]` |
| `method` | `RequestMethod` |

## Diagram

```mermaid
graph LR
  A[RequestMappingMetadata] --> B[path: string | string[]]
  A --> C[method: RequestMethod]
  B --> D[Single route path]
  B --> E[Multiple route paths]
  C --> F[HTTP verb]
  F --> G[Router registration]
```

## Usage

```ts
import { RequestMethod } from '@nestjs/common';
import type { RequestMappingMetadata } from './request-mapping.decorator';

const mapping: RequestMappingMetadata = {
  path: ['/users', '/accounts'],
  method: RequestMethod.GET,
};

// Example decorator metadata consumed by the HTTP router.
function registerRoute(metadata: RequestMappingMetadata) {
  for (const path of Array.isArray(metadata.path)
    ? metadata.path
    : [metadata.path]) {
    console.log(`Registering ${RequestMethod[metadata.method]} ${path}`);
  }
}

registerRoute(mapping);
```

## AI Coding Instructions

- Use `path` as a string for a single route or a string array when the same handler supports multiple routes.
- Always provide a valid `RequestMethod` enum value; do not use raw HTTP method strings unless converted first.
- Normalize `path` to an array before iterating over route mappings in router integration code.
- Keep this metadata focused on route path and HTTP method; add unrelated handler metadata through separate interfaces or decorators.

## How it works

- **`RequestMappingMetadata`** is an exported TypeScript interface used as the `metadata` argument type for the `RequestMapping` method-decorator factory. It declares two optional fields: `path`, a string or string array, and `method`, a `RequestMethod` enum member. [packages/common/decorators/http/request-mapping.decorator.ts:4-7](packages/common/decorators/http/request-mapping.decorator.ts#L4-L7) [packages/common/decorators/http/request-mapping.decorator.ts:14-16](packages/common/decorators/http/request-mapping.decorator.ts#L14-L16)

- `path` corresponds to the `PATH_METADATA` key, whose string value is `'path'`; `method` corresponds to `METHOD_METADATA`, whose string value is `'method'`. [packages/common/constants.ts:10](packages/common/constants.ts#L10) [packages/common/constants.ts:17](packages/common/constants.ts#L17)

- Its `method` type is the `RequestMethod` enum. The enum contains `GET`, `POST`, `PUT`, `DELETE`, `PATCH`, `ALL`, `OPTIONS`, `HEAD`, `SEARCH`, and WebDAV-related members through `UNLOCK`. [packages/common/enums/request-method.enum.ts:1-18](packages/common/enums/request-method.enum.ts#L1-L18)

- When passed to `RequestMapping`, a non-empty `path` value is retained; an omitted path, empty string, or empty array becomes `'/'`. An omitted or falsy `method` becomes `RequestMethod.GET`. [packages/common/decorators/http/request-mapping.decorator.ts:9-19](packages/common/decorators/http/request-mapping.decorator.ts#L9-L19) The decorator writes the resulting path and request method as reflection metadata on the decorated method’s function (`descriptor.value`). [packages/common/decorators/http/request-mapping.decorator.ts:21-29](packages/common/decorators/http/request-mapping.decorator.ts#L21-L29)

- The interface contains no runtime validation or error handling itself. Its observable runtime effect occurs only through `RequestMapping`, which calls `Reflect.defineMetadata` for both keys. [packages/common/decorators/http/request-mapping.decorator.ts:4-7](packages/common/decorators/http/request-mapping.decorator.ts#L4-L7) [packages/common/decorators/http/request-mapping.decorator.ts:26-27](packages/common/decorators/http/request-mapping.decorator.ts#L26-L27)

- During controller route discovery, the stored path and method metadata are read from the prototype method. A string path is converted to a one-element path array after adding a leading slash; an array is mapped the same way per element. If no path metadata exists, that method is not treated as a route. [packages/core/router/paths-explorer.ts:53-82](packages/core/router/paths-explorer.ts#L53-L82)