MongoDB Driver Not Being Recognized

Question

I'm building an express app that uses MongoDB for its back end but when I make a request to the database in other parts of the app it's not being recognized.

Here's what I have:

APP.JS (Using Paul's Answer):

var express = require('express');
var app = express();
var bodyParser = require('body-parser');
var cookieParser = require('cookie-parser');
var passport = require('passport');
var mongo = require('mongodb').MongoClient;
var assert = require('assert');

// make mongodb available to the application
app.use((req, res, next) => {
  mongo.connect('mongodb://localhost:27017/formulas', (e, db) => {
  if (e) return next(e);
  req.db = db;
  next();
});

// cleanup
  req.on('end', () => { req.db.close(); });
});

//define routes
var root = require('./routes/index');
var authenticate = require('./routes/authenticate');
var about = require('./routes/about');
var contact = require('./routes/contact');
var formula = require('./routes/formula');
var formulaAPI = require('./routes/api/formula');
var formulaList = require('./routes/formula-list');
var formulaListAPI = require('./routes/api/formula-list');

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

app.use(root);
app.use(about);
app.use(contact);
app.use(formula);
app.use(formulaAPI);
app.use(formulaList);
app.use(formulaListAPI);
app.use(authenticate);

app.listen(3000, function(){
  console.log("The server is now listening on port 3000");
});

module.exports = app;

When I call the database through a route like this:

var app = require('express');
var router = app.Router();
var data = require('../data/formula.json');

router.get('/formula-list', function(req, res){
var db = req.db;
db.formulas.find({}, {}, function(e, docs){
  res.render('formula-list', {
    formulas: docs,
    title: 'Your Formulas',
    description: `List of saved user formulas from the formula generator`,
    ID: 'formula-list',
    keywords: 'formula generator, health kismet, nutraceutical formula 
  builder'
  });
});
});

I get the following error:

TypeError: Cannot read property 'find' of undefined

When I do a console.log(req.db) I get the following in my console:

req.db:

EventEmitter {
domain: null,
_events: {},
_eventsCount: 0,
_maxListeners: undefined,
s:
 { databaseName: 'formulas',
 dbCache: {},
 children: [],
 topology:
  EventEmitter {
    domain: null,
    _events: [Object],
    _eventsCount: 7,
    _maxListeners: undefined,
    clientInfo: [Object],
    s: [Object] },
 options:
  { readPreference: [Object],
    promiseLibrary: [Function: Promise] },
 logger: { className: 'Db' },
 bson: {},
 authSource: undefined,
 readPreference:
  { _type: 'ReadPreference',
    mode: 'primary',
    tags: undefined,
    options: undefined },
 bufferMaxEntries: -1,
 parentDb: null,
 pkFactory: undefined,
 nativeParser: undefined,
 promiseLibrary: [Function: Promise],
 noListener: false,
 readConcern: undefined },
 serverConfig: [Getter],
 bufferMaxEntries: [Getter],
 databaseName: [Getter] }

Answer 1

Going by the documentation on npm, I can see that to access a particular collection, this is what you have to do:

1. Select the collection on which you want to perform the operation
2. Perform the operation

Here is the code example:

router.get('/formula-list', function(req, res) {

  // Select the collection on which you want to perform an operation
  var formulas = req.db.collection('formulas');

  // Perform that operation
  formulas.find({}, {}, function(e, docs) {

    res.render('formula-list', {
      formulas: docs,
      title: 'Your Formulas',
      description: `List of saved user formulas from the formula generator`,
      ID: 'formula-list',
      keywords: 'formula generator, health kismet, nutraceutical formula builder'
    });
  });
});

Answer 2

OK, so before declaring the first route that needs the connection, you'll want to wire up your middleware to assign the db connection to the request. Probably a good idea to release the resource again after the response is sent as well, unless you're using connection pooling.

app.use((req, res, next) => {
  mongo.connect('mongodb://localhost:27017/formulas', (e, db) => {
    if (e) return next(e);
    req.db = db;
    next();
  });

  // cleanup
  req.on('end', () => { req.db.close(); });
});

Hope that helps.