NodeJS/ MongoDB - UnhandledPromiseRejectionWarning: Unhandled promise rejection (rejection id: 1): Error: invalid schema, expected mongodb

I am currently building an app using MEAN stack. For which i have a form and need to insert the form data into the mongoDB database.

But i get the error "(node:1888) UnhandledPromiseRejectionWarning: Unhandled promise rejection (rejection id: 1): Error: invalid schema, expected mongodb connected to db NaN".

and also TypeError: Cannot read property 'insert' of undefined at C:\Users\Avvijan\meanexamples\appointment\routes\main.js:64:12

please help!

My code snippet is

    <form class = "profile" action = "/process" method="post">
        <div class="form-group">
            <label for="Fname">First Name: </label>
            <input type="text" id="fName" name = "fName" class="form-control" placeholder="first name" >
        </div>
        <div class="form-group">
            <label for="Lname">Last Name: </label>
            <input type="text" id="lName" name = "lName" class="form-control" placeholder="last name" >
        </div>
        <div class="form-group">
            <label for="email">Email : </label>
            <input type="email" id="email" name = "email" class="form-control" placeholder="email.." required>
        </div>
        <button type="submit" class="btn btn-primary" id="save">Submit</button>
    </form>

and my routes->main.js file is

    var express = require('express');
    var router = express.Router();
    var mongoose = require('mongoose');
    const config = require('../config/database');
    var mongo = require('mongodb');
    var dburl = "mongodb://localhost:27017/appointment";
    var db = mongo('appointment',['appoint']);
    //connect to db
    mongoose.connect(config.database);
    //check connection
    mongoose.connection.on("connected",function(){
    console.log('connected to db',+config.database);
    }); 
    mongoose.connection.on("error",function(err){
    console.log("error",+err);
    });
router.post('/process',function(req,res){
var newClient = {
 firstName : req.body.fName,
 lastName : req.body.lName,
 email : req.body.email,
 phone : req.body.phone,
 dob : req.body.dob,
 gender : req.body.gender,
};
db.appoint.insert(newClient,function(err,result){
    if(err) {   throw err; }
    else{
        res.redirect('/thanks');
    }
});

console.log("firstName:" +req.body.fName);
console.log("lastName:"+req.body.lName);
console.log('email:'+req.body.email);

});

Please advice what is the mistake im making here. :( Thanks in advance. Regards, Janani

via janani