java video tutorial by venketesh

https://www.youtube.com/watch?v=1OpAgZvYXLQ

send email through codeigniter

https://stackoverflow.com/questions/18586801/send-email-by-using-codeigniter-library-via-localhost

$facet in mongodb

https://thecodebarbarian.com/a-nodejs-perspective-on-mongodb-34-facet.html