# ParamsTokenFactory

**Kind:** Class

**Source:** [`packages/core/pipes/params-token-factory.ts`](https://github.com/nestjs/nest/blob/master/packages/core/pipes/params-token-factory.ts#L4)

**Part of:** [Core](subsystem-packages-core)

`ParamsTokenFactory` normalizes route parameter metadata by converting known `RouteParamtypes` enum values into their string token equivalents. It is used by the pipes system to provide consistent parameter identifiers when resolving and applying pipes to controller arguments.

## Methods

| Method | Signature | Returns |
|---|---|---|
| `exchangeEnumForString` | `exchangeEnumForString(type: RouteParamtypes)` | `Paramtype` |

## Diagram

```mermaid
graph LR
  A[Route parameter metadata] --> B[ParamsTokenFactory]
  B --> C[exchangeEnumForString]
  C --> D[String parameter token]
  D --> E[Pipes context / parameter resolution]
```

## Usage

```ts
import { ParamsTokenFactory } from '@nestjs/core/pipes/params-token-factory';
import { RouteParamtypes } from '@nestjs/common/enums/route-paramtypes.enum';

const paramsTokenFactory = new ParamsTokenFactory();

const token = paramsTokenFactory.exchangeEnumForString(
  RouteParamtypes.BODY,
);

console.log(token); // "body"
```

## AI Coding Instructions

- Use `exchangeEnumForString()` when pipe-related code needs a stable string token for a route parameter type.
- Preserve existing enum-to-string mappings when adding or modifying supported parameter types.
- Return unrecognized parameter values unchanged so custom or already-normalized tokens remain compatible.
- Keep this factory focused on token normalization; pipe execution and parameter extraction belong in their respective context creators.

## Relationships

- IMPORTS → `Paramtype`
- IMPORTS → `RouteParamtypes`