# MulterModuleAsyncOptions

**Kind:** Interface

**Source:** [`packages/platform-express/multer/interfaces/files-upload-module.interface.ts`](https://github.com/nestjs/nest/blob/master/packages/platform-express/multer/interfaces/files-upload-module.interface.ts#L16)

**Part of:** [Platform Express](subsystem-packages-platform-express)

`MulterModuleAsyncOptions` configures Multer asynchronously when registering NestJS file upload support. It allows upload options to be provided by an existing provider, a dedicated options factory class, or an inline factory function with dependency injection.

## Properties

| Property | Type |
|---|---|
| `useExisting` | `Type<MulterOptionsFactory>` |
| `useClass` | `Type<MulterOptionsFactory>` |
| `useFactory` | `( ...args: any[] ) => Promise<MulterModuleOptions> | MulterModuleOptions` |
| `inject` | `any[]` |

## Diagram

```mermaid
graph LR
  A[MulterModuleAsyncOptions] --> B[useExisting]
  A --> C[useClass]
  A --> D[useFactory]
  A --> E[inject]

  B --> F[MulterOptionsFactory]
  C --> F
  D --> G[MulterModuleOptions]
  E --> D
  F --> G
  G --> H[MulterModule.registerAsync]
```

## Usage

```ts
import { Module } from '@nestjs/common';
import {
  MulterModule,
  MulterModuleAsyncOptions,
  MulterOptionsFactory,
} from '@nestjs/platform-express';
import { ConfigService } from '@nestjs/config';
import { diskStorage } from 'multer';

const multerOptions: MulterModuleAsyncOptions = {
  inject: [ConfigService],
  useFactory: async (configService: ConfigService) => ({
    storage: diskStorage({
      destination: configService.get<string>('UPLOAD_DIRECTORY', './uploads'),
      filename: (_request, file, callback) => {
        callback(null, `${Date.now()}-${file.originalname}`);
      },
    }),
    limits: {
      fileSize: 5 * 1024 * 1024,
    },
  }),
};

@Module({
  imports: [MulterModule.registerAsync(multerOptions)],
})
export class AppModule {}
```

## AI Coding Instructions

- Use exactly one configuration strategy: `useExisting`, `useClass`, or `useFactory`.
- Add required dependencies to `inject` when using `useFactory`; their order must match the factory function parameters.
- Return a valid `MulterModuleOptions` object from the factory, either synchronously or as a `Promise`.
- Prefer `useExisting` when an existing `MulterOptionsFactory` provider should be reused; use `useClass` when Nest should create a dedicated factory provider.
- Configure storage, file-size limits, and file filtering in the returned Multer options rather than directly in controllers.

## How it works

`MulterModuleAsyncOptions` is the public TypeScript configuration shape accepted by `MulterModule.registerAsync()`. It extends only the `imports` member of `ModuleMetadata`; its remaining members select how the module resolves `MulterModuleOptions`. `MulterModuleOptions` is an alias for `MulterOptions`. [files-upload-module.interface.ts:4](packages/platform-express/multer/interfaces/files-upload-module.interface.ts#L4) [files-upload-module.interface.ts:16-25](packages/platform-express/multer/interfaces/files-upload-module.interface.ts#L16-L25) [multer.module.ts:30](packages/platform-express/multer/multer.module.ts#L30)

- `imports` is optional through the inherited `ModuleMetadata.imports` member and is copied to the dynamic module’s `imports` field. [files-upload-module.interface.ts:16-19](packages/platform-express/multer/interfaces/files-upload-module.interface.ts#L16-L19) [multer.module.ts:31-34](packages/platform-express/multer/multer.module.ts#L31-L34)
- `useFactory` may be a function with arbitrary injected arguments that returns `MulterModuleOptions` directly or as a promise. When present, it becomes the factory for the `MULTER_MODULE_OPTIONS` provider. [files-upload-module.interface.ts:22-25](packages/platform-express/multer/interfaces/files-upload-module.interface.ts#L22-L25) [multer.module.ts:63-68](packages/platform-express/multer/multer.module.ts#L63-L68)
- `inject` supplies that factory’s dependency tokens. When `useFactory` is selected and `inject` is absent, the module uses an empty array. [files-upload-module.interface.ts:25](packages/platform-express/multer/interfaces/files-upload-module.interface.ts#L25) [multer.module.ts:63-68](packages/platform-express/multer/multer.module.ts#L63-L68)
- `useExisting` names an existing class-type token for a `MulterOptionsFactory`. The options provider injects that token and calls its `createMulterOptions()` method. That method may return options directly or asynchronously. [files-upload-module.interface.ts:9-11](packages/platform-express/multer/interfaces/files-upload-module.interface.ts#L9-L11) [files-upload-module.interface.ts:20](packages/platform-express/multer/interfaces/files-upload-module.interface.ts#L20) [multer.module.ts:70-75](packages/platform-express/multer/multer.module.ts#L70-L75)
- `useClass` names a class-type `MulterOptionsFactory`. In the absence of `useExisting` and `useFactory`, the module registers the class as a provider, injects it into the options provider, and calls `createMulterOptions()`. [files-upload-module.interface.ts:9-11](packages/platform-express/multer/interfaces/files-upload-module.interface.ts#L9-L11) [files-upload-module.interface.ts:21](packages/platform-express/multer/interfaces/files-upload-module.interface.ts#L21) [multer.module.ts:48-57](packages/platform-express/multer/multer.module.ts#L48-L57) [multer.module.ts:70-75](packages/platform-express/multer/multer.module.ts#L70-L75)

`useFactory` takes precedence when it is set: the options-provider construction checks it first. A set `useExisting` also prevents registration of `useClass`; the injected factory token then selects `useExisting` before `useClass`. [multer.module.ts:48-49](packages/platform-express/multer/multer.module.ts#L48-L49) [multer.module.ts:63-75](packages/platform-express/multer/multer.module.ts#L63-L75)

All members declared directly by this interface are optional, and the visible implementation contains no explicit validation or thrown error for a configuration with none of `useFactory`, `useExisting`, or `useClass`. In that case, its class branch constructs a provider whose token and injection entry are `undefined`. [files-upload-module.interface.ts:20-25](packages/platform-express/multer/interfaces/files-upload-module.interface.ts#L20-L25) [multer.module.ts:48-57](packages/platform-express/multer/multer.module.ts#L48-L57) [multer.module.ts:70-75](packages/platform-express/multer/multer.module.ts#L70-L75)

Calling `registerAsync` constructs a dynamic module that exports `MULTER_MODULE_OPTIONS` and adds a generated `MULTER_MODULE_ID` value provider. [multer.module.ts:30-42](packages/platform-express/multer/multer.module.ts#L30-L42)