How do I fix Multer-Gridfs-Storage error "Error creating storage engine. At least one of url or db option must be provided"?

Question

As I am trying to deploy my app to Heroku, I get the error "Error creating storage engine. At least one of url or db option must be provided." in my heroku logs. However, I get no errors while developing and testing the app in my IDE.

Here is my error log:

...
2020-10-17T05:24:18.106601+00:00 app[web.1]: Error: Error creating storage engine. At least one of url or db option must be provided.
2020-10-17T05:24:18.106602+00:00 app[web.1]: at new GridFSStorage (/app/node_modules/multer-gridfs-storage/lib/gridfs.js:59:10)
2020-10-17T05:24:18.106602+00:00 app[web.1]: at Object.<anonymous> (/app/config/multer.js:7:17)
2020-10-17T05:24:18.106603+00:00 app[web.1]: at Module._compile (internal/modules/cjs/loader.js:1015:30)
2020-10-17T05:24:18.106604+00:00 app[web.1]: at Object.Module._extensions..js (internal/modules/cjs/loader.js:1035:10)
2020-10-17T05:24:18.106604+00:00 app[web.1]: at Module.load (internal/modules/cjs/loader.js:879:32)
2020-10-17T05:24:18.106605+00:00 app[web.1]: at Function.Module._load (internal/modules/cjs/loader.js:724:14)
2020-10-17T05:24:18.106605+00:00 app[web.1]: at Module.require (internal/modules/cjs/loader.js:903:19)
2020-10-17T05:24:18.106605+00:00 app[web.1]: at require (internal/modules/cjs/helpers.js:74:18)
2020-10-17T05:24:18.106606+00:00 app[web.1]: at Object.<anonymous> (/app/server.js:9:16)
2020-10-17T05:24:18.106607+00:00 app[web.1]: at Module._compile (internal/modules/cjs/loader.js:1015:30)
...

Here is my code for multer:

require('dotenv').config();
const path = require('path');
const crypto = require('crypto');
const multer  = require('multer');
const GridFsStorage = require('multer-gridfs-storage');

const storage = new GridFsStorage({
  url: process.env.URI,
  options: { useUnifiedTopology: true },
  file: (req, file) => {
    return new Promise((resolve, reject) => {
      crypto.randomBytes(16, async (err, buf) => {
        if (err) return reject(err);

        const filename = buf.toString('hex') + path.extname(file.originalname);

        const fileInfo = { filename, bucketName: 'uploads' };
        
        resolve(fileInfo);
      });
    });
  }
});

const upload = multer({ storage });

module.exports = upload;

My process.env.URI variable is in the form: URI=mongodb+srv://...

Any help is greatly appreciated :)

Answer 1

I found the error was actually due to my environment variables. I had to set them up in Heroku for the application to read them (I was relying on my .env file, but of course the .gitignore file will prevent the file from being pushed to Heroku master).

Answer 2

For someone using mongodb as database. I am using the mongodb connection string and I refer to it via .env variable. Since .gitignore is not pushing this .env variable, it happens that this connection string is missing. You can fix this by basically adding your connection string back into your .env file.