What is the best practice for using MongoClient.connect in an Express app with lots of routers?

Question

I have an app that does this kind of thing multiple times:

app.get('/', function(req, res){
  MongoClient.connect(dbUrl, function(err, db){
    //work with db data
  });
});

But then I heard somewhere that it's better practice to connect to the database once, and use that connection on the whole thing. So does that mean something like this?:

MongoClient.connect(dbUrl, function(err, db){
  app.get('/', function(req, res){
    //do some stuff
  });        
  app.get('/other', function(req, res){
    //do some stuff
  });
  //
  //more routers....
  //
});

So which of these two methods would be considered better practice? And what makes it better? What is the difference? And is there a better way?

Answer 1

Connect once, watch for connection errors:

mongoose.connect(MONGO_URI);
var dbConnection = mongoose.connection;
dbConnection.on('error', console.error.bind(console, 'connection error...'));
dbConnection.once('open', function callback() { console.log('DB opened'); });

Use dbConnection when you need to database access.