如果前端文件字段为空，如何不覆盖MySql列

Question

我正在使用以下控制器 exports.update 在我的 CRUD 应用上上传数据和文件。我遇到了一个大问题，我需要帮助/建议。

在客户端，如果上传文件字段，例如covid_19D 保持为空，但填充了其他值并提交了 post 请求，文件空字段覆盖 covid_19D MySql 数据库列，删除先前输入的文件名并将 covid_19D MySql 列值留空。

我该如何解决这个问题？如果客户端提交了post请求，file字段为空，不覆盖MySql列之前加载的文件名？

这是我的前端： crew-forms.hbs

<div class="row">

      {{!-- covid-19 vaccination --}}

      <div class="col-md-6 mt-5">
        <br>

        <input class="form-control" type="text" placeholder="COVID-19 VACCINATION CERTIFICATES" aria-label="readonly input example" readonly data-bs-trigger="focus" role="button" data-bs-toggle="popover" title="Covid-19 vaccination certificate.">
      </div>

      <div class="col-md-6 mt-5">
        <br>
        <input type="text" id="datepickercovid_19" value="{{this.covid_19}}" placeholder="iss. date (mm/dd/yyyy)" name='covid_19'>
      </div>

      {{!-- input file covid_19 --}}
      <div class="col-md-6">

        <br>

        <input type="file" name="covid_19D" multiple id="file_box" value="{{this.covid_19D}}" />

和编辑-crew.hbs

{{#each rows}}
<form class="row g-1 needs-validation" method="POST" action="/editcrew/{{this.id}}" encType="multipart/form-data" novalidate>
  {{> crew-form}}
</form>
{{/each}}

这里是 userController.js

exports.update = async(req, res) => {

  try {
    await upload(req, res);

    // --FILE HANDLING BLOCKCODE---

    var find = JSON.parse(JSON.stringify(req.files)); //  to remove Object:null prototype
    // conditional statments to hanlde the front end file existence.

    if (find.hasOwnProperty('covid_19D') == false) {
      var covid_19D = ""
    } else {
      var covid_19D = find.covid_19D[0].filename

    }


    if (find.hasOwnProperty('fitnessD') == false) {
      var fitnessD = ""
    } else {
      var fitnessD = find.fitnessD[0].filename
    }



  } catch (error) {
    console.log(error);

    if (error.code === "LIMIT_UNEXPECTED_FILE") {

      return res.send("Too many files to upload.");
    }
    // return res.send(`Error when trying upload many files: ${error}`);
  }



  // ---DATA ENTERING BLOCK CODE---

  var post = req.body;
  var first_name = post.first_name;
  var last_name = post.last_name;
  var email = post.email;
  var phone = post.phone;
  var coc = post.coc;
  var expiration = post.expiration;
  var covid_19 = post.covid_19;
  var fitness = post.fitness;
  var yellowF = post.yellowF;





  connection.query('UPDATE user SET first_name=? ,last_name=?, email=?, phone=?, coc=?, expiration=?, covid_19=?,covid_19D=? , fitness=? ,fitnessD=?  WHERE id = ?', [first_name, last_name, email, phone, coc, expiration, covid_19, covid_19D, fitness, fitnessD, req.params.id],
    (err, rows) => {

      if (!err) {
        connection.query('SELECT * FROM user WHERE id = ?', [req.params.id], (err, rows) => {
          if (!err) {
            res.render('edit-crew', {
              rows,
              alert: `${first_name} has been updated.`
            });

          } else {
            console.log(err);
          }
          // console.log('The data from user table:\n', rows);
        });
      } else {
        console.log(err);
      }
      // console.log('The data from user table:\n', rows);
    });

}

这是我的app.js

const express = require("express");
const exphbs = require("express-handlebars");
const path = require('path');
bodyParser = require("body-parser");
// to be removed when deployed in heroku

require("dotenv").config();
const cookieParser = require('cookie-parser');



// Parsing middleware
const app = express();



//to load static file
app.use(express.static("public"));
// app.use(express.static("upload"));
//Listen on port 5000
app.use(express.urlencoded({
  extended: true
})); //To parse URL-encoded bodies (as sent by HTML forms) set from false to true as per bezkoder tutorial

app.use(express.json()); //To parse the incoming requests with JSON bodies
app.use(cookieParser());

app.engine("hbs", exphbs({
  extname: ".hbs"
})); //Templating engine to change the extenion of file from .handlebar to .hbs
app.set("view engine", "hbs");



app.use("/", require('./routes/user'));
app.use('/auth', require('./routes/auth'));


app.set('views', __dirname + '/views');
app.use(bodyParser.urlencoded({
  extended: false
}));
app.use(bodyParser.json());
app.use(express.static(path.join(__dirname, 'public')));


const port = process.env.PORT || 5000;
app.listen(port, () => console.log(`Listening on port ${port}`));

提前感谢您在正确路径上的任何建议重定向！

Answer 1

好的，我明白了！

我只是简单地从前端的数据库中调用存储的文件名，并使用 req.body.covid_19D 来发布变量的名称。

这里是代码sn-p：

 try {
        await upload(req, res);
        // --FILE HANDLING BLOCKCODE---
        var find = JSON.parse(JSON.stringify(req.files));//  to remove Object:null prototype
        // conditional statments to hanlde the front end file existence.
        if (find.hasOwnProperty('covid_19D') == false) {
            var covid_19D = req.body.covid_19D
        } else {
            var covid_19D = find.covid_19D[0].filename

        }