title: missing db argument error when connecting gridfs multer and mongodb
body: <p>I am using gridfs and mutler to upload files likes ppt pdf etc..to mongodb atlas. When setting up router its keeps saying db not found I have my uri in a config file.What am i missing here in mongodb atlas i have 3 collections in a database called 'test' do i have to create another db in the cluster? Please help</p>
  
  <blockquote>
    <blockquote>
      <p>if (!db) throw new Error('missing db argument\nnew Grid(db, mongo)');
                 ^</p>
    </blockquote>
    
    <p>Error: missing db argument new Grid(db, mongo)
        at new Grid (/Users/ezana/Desktop/Canvas/backend/node_modules/gridfs-stream/lib/index.js:25:18)
        at Grid (/Users/ezana/Desktop/Canvas/backend/node_modules/gridfs-stream/lib/index.js:19:12)
        at Object. (/Users/ezana/Desktop/Canvas/backend/api/routes/fileUploadRoutes.js:9:11)
        at Module._compile (internal/modules/cjs/loader.js:701:30)
        at Object.Module._extensions..js (internal/modules/cjs/loader.js:712:10)
        at Module.load (internal/modules/cjs/loader.js:600:32)
        at tryModuleLoad (internal/modules/cjs/loader.js:539:12)
        at Function.Module._load (internal/modules/cjs/loader.js:531:3)
        at Module.require (internal/modules/cjs/loader.js:637:17)
        at require (internal/modules/cjs/helpers.js:22:18)
        at Object. (/Users/ezana/Desktop/Canvas/backend/app.js:7:21)
        at Module._compile (internal/modules/cjs/loader.js:701:30)
        at Object.Module._extensions..js (internal/modules/cjs/loader.js:712:10)
        at Module.load (internal/modules/cjs/loader.js:600:32)
        at tryModuleLoad (internal/modules/cjs/loader.js:539:12)
        at Function.Module._load (internal/modules/cjs/loader.js:531:3)</p>
  </blockquote>
  
  <pre><code>const router = require('express').Router();
  const multer = require('multer');
  const db = require('./config/main').mongoURI;
  const {
      mongo,
      connection
  } = require('mongoose');
  const Grid = require('gridfs-stream');
  Grid.mongo = mongo;
  const gfs = Grid(connection.db);
  
  const storage = require('multer-gridfs-storage')({
      db: connection.db,
      file: (req, file) =&gt; {
          return {
              filename: file.originalname
          }
      }
  });
  </code></pre>