javascript - multer 单个上传不起作用，但数组可以工作

Question

我正在使用 React js 上传单个文件。但是 multer.single() 不起作用，而 multer.array() 起作用。有什么问题吗？

//Node.js
const upload = multer({
    storage: multer.diskStorage({
        destination: './uploads',
        filename: (_, file, cb) => cb(null, file.originalname),
    }),
});
// app.use(upload.array('pdf')); // works
app.use(upload.single('pdf')); // not working

使用单一方法时的错误是

(node:6096) UnhandledPromiseRejectionWarning: TypeError: Cannot read property '0' of undefined
    at convertToJPG (D:\Projects\Node\pdf2pic\controllers\convert.js:9:44)
    at Layer.handle [as handle_request] (D:\Projects\Node\pdf2pic\node_modules\express\lib\router\layer.js:95:5)
    at next (D:\Projects\Node\pdf2pic\node_modules\express\lib\router\route.js:137:13)
    at Route.dispatch (D:\Projects\Node\pdf2pic\node_modules\express\lib\router\route.js:112:3)
    at Layer.handle [as handle_request] (D:\Projects\Node\pdf2pic\node_modules\express\lib\router\layer.js:95:5)
    at D:\Projects\Node\pdf2pic\node_modules\express\lib\router\index.js:281:22
    at Function.process_params (D:\Projects\Node\pdf2pic\node_modules\express\lib\router\index.js:335:12)
    at next (D:\Projects\Node\pdf2pic\node_modules\express\lib\router\index.js:275:10)
    at Function.handle (D:\Projects\Node\pdf2pic\node_modules\express\lib\router\index.js:174:3)
    at router (D:\Projects\Node\pdf2pic\node_modules\express\lib\router\index.js:47:12)
(Use `node --trace-warnings ...` to show where the warning was created)
(node:6096) UnhandledPromiseRejectionWarning: Unhandled promise rejection. This error originated either by throwing inside of an async function without a catch block, or by rejecting a promise which was not handled with .catch(). To terminate the node process on unhandled promise rejection, use the CLI flag `--unhandled-rejections=strict` (see https://nodejs.org/api/cli.html#cli_unhandled_rejections_mode). (rejection id: 1)
(node:6096) [DEP0018] DeprecationWarning: Unhandled promise rejections are deprecated. In the future, promise rejections that are not handled will terminate the Node.js process with a non-zero exit code.

客户端代码是

<input
          accept=".pdf"
          multiple={false}
          name="pdf"
          onChange={onChangeHandler}
          ref={fileInputRef}
          style={{ display: 'none' }}
          type="file"
        />

    const onChangeHandler = (event: React.ChangeEvent<HTMLInputElement>) => {
      if (!event.target.files?.length) {
        return;
      }
  
      const formData = new FormData();  
      Array.from(event.target.files).forEach((file) => {
        formData.append(event.target.name, file);
      });
  
      props.onChange(formData);
  
      formRef.current?.reset();
    };

我在这里做错了什么？

Answer 1

使用 multer 处理单个文件上传与多个文件上传之间的主要区别在于文件所在的位置:

• upload.single() -> req.file
• upload.array()(和upload.fields())-> req.files

如果不在代码中进一步考虑此更改，则无法从多个交换为单个。

从错误消息来看，在 convert.js 文件(第 9 行第 44 列)中，您无法读取数组的第一个元素 req.files 。这是因为 req.files 不存在，您应该使用 req.file 而不是它，它是一个对象。

此免费指南 Parsing Requests in Node.js将帮助您在 Node.js 中处理文件上传时修复这些类型的错误。