MulterField

Kind: Interface

Source: packages/platform-express/multer/interfaces/multer-options.interface.ts

Part of: Platform Express

MulterField defines a named multipart form-data field accepted by NestJS's Multer integration. It is typically used when configuring file upload interceptors that accept multiple named file fields, with maxCount limiting how many files each field may contain.

Properties

Diagram

mermaid
graph LR
  Client[Multipart Request] --> Interceptor[FileFieldsInterceptor]
  Interceptor --> Field[MulterField]
  Field --> Name["name: field identifier"]
  Field --> MaxCount["maxCount: maximum files"]
  Interceptor --> Uploads[Uploaded file arrays]

Usage

ts
import { Controller, Post, UploadedFiles, UseInterceptors } from '@nestjs/common';
import { FileFieldsInterceptor } from '@nestjs/platform-express';
import type { MulterField } from '@nestjs/platform-express/multer/interfaces/multer-options.interface';

const uploadFields: MulterField[] = [
  { name: 'avatar', maxCount: 1 },
  { name: 'documents', maxCount: 5 },
];

@Controller('uploads')
export class UploadController {
  @Post()
  @UseInterceptors(FileFieldsInterceptor(uploadFields))
  uploadFiles(
    @UploadedFiles()
    files: {
      avatar?: Express.Multer.File[];
      documents?: Express.Multer.File[];
    },
  ) {
    return {
      avatar: files.avatar?.[0],
      documents: files.documents ?? [],
    };
  }
}

AI Coding Instructions

• Use name values that exactly match the multipart form field names sent by clients.
• Set maxCount to the intended per-field upload limit; use 1 for single-file fields.
• Pass MulterField[] to FileFieldsInterceptor when an endpoint accepts several differently named file fields.
• Remember that uploaded files are returned as arrays per field, including fields configured with maxCount: 1.
• Configure Multer validation, storage, and file-size limits separately through interceptor options or module configuration.