Mongoose connection best practices

1_mongoose.js

var db = mongoose.connect('mongodb://localhost:27017/DB'); 

// In middleware
app.use(function (req, res, next) {

  // action after response
  var afterResponse = function() {
   logger.info({req: req}, "End request");

    // any other clean ups
    mongoose.connection.close(function () {
      console.log('Mongoose connection disconnected');
    });
  }
  
  // hooks to execute after response
  res.on('finish', afterResponse);
  res.on('close', afterResponse);

  // do more stuff

  next();
}

connect-mongo_session_store.js

var express = require('express');
var MongoStore = require('connect-mongo')(express);

app.use(express.session({
  secret: settings.cookie_secret,
  store: new MongoStore({
    "db": "dbName",
    "host": "localhost",
    "port": "27017",
    "collection": "mysessions",
    "clear_interval": 3600,
    "auto_reconnect": true
  })
}));

connect-mongo_use_mongoose_conn1.js

new MongoStore({
  db: mongoose.connection.db
})

connect-mongo_use_mongoose_conn2.js

new MongoStore({
  mongoose_connection : mongoose.connections[0],
})

mocha_tests.js

var mongoose = require('mongoose');

describe('My test', function() {
  before(function(done) {
    //Another possibility is to check if mongoose.connection.readyState equals 1
    if (mongoose.connection.db) return done();
    mongoose.connect('mongodb://localhost/puan_test', done);
  });
});

// You can put one ‘after()’ statement above all else that will run when all tests are finished
after(function(done){
  db.connection.db.dropDatabase(function(){
    db.connection.close(function(){
      done();
    });
  });
});

model_close_conn.js

var db = mongoose.connect('mongodb://localhost:27017/DB'); 
Model.findOne({}, function () {

  // do your stuff

  // For any weird reason you want to close connection everytime
  db.disconnect();
});

mongoose_connet.js

var mongoose   = require('mongoose');
var express    = require('express');

var config     = require('./config/config');

var db_server  = process.env.DB_ENV || 'primary';

mongoose.connection.on("connected", function(ref) {
  console.log("Connected to " + db_server + " DB!");
  
  var app = express();

  // add your middleware set-up
  // add your routes
  
  port = process.env.port || 3000;
  ip = process.env.ip;
  
  app.listen(port, ip, function() {
  console.log('listening on port ' + port);
  });
});

// If the connection throws an error
mongoose.connection.on("error", function(err) {
  console.error('Failed to connect to DB ' + db_server + ' on startup ', err);
});

// When the connection is disconnected
mongoose.connection.on('disconnected', function () {
  console.log('Mongoose default connection to DB :' + db_server + ' disconnected');
});

var gracefulExit = function() { 
  mongoose.connection.close(function () {
    console.log('Mongoose default connection with DB :' + db_server + ' is disconnected through app termination');
    process.exit(0);
  });
}

// If the Node process ends, close the Mongoose connection
process.on('SIGINT', gracefulExit).on('SIGTERM', gracefulExit);

try {
  options.server.socketOptions = options.replset.socketOptions = { keepAlive: 1 };
  mongoose.connect(config.getDBURL(db_server));
  console.log("Trying to connect to DB " + db_server);
} catch (err) {
  console.log("Sever initialization failed " , err.message);
}

mongostore_conn.js

mongoose.connect(config.db, {auto_reconnect: true, native_parser: true}, function(err) {
    var MongoStore = require("connect-mongodb");
    
    var app = express();
    app.use(express.session({
        cookie: {maxAge: 60000 * 20},
        secret: "secret",
        store: new MongoStore({db: mongoose.connection.db})
    }));
});

According to the Mongoose FAQ:

Q. Should I create/destroy a new connection for each database operation?
A. No. Open your connection when your application starts up and leave it open until the application shuts down.
It looks like there are two camps.