TypeError: db.collection is not a function, CANNOT GET

incorect syntax, you must read property of db.collection, but you call that. Example:

db.collection['products']!!!db.collection['text'].save({        title: title,        author: author,        text: text    }, callback);};module.exports.findBookByTitle = function (db, title, callback) {    db.collection['text'].findOne({        title: title    }, function (err, doc) {        if (err || !doc) callback(null);        else callback(doc.text);    });};module.exports.findProductsByName = function (db, name, callback) {    db.collection['products'].findOne({

For example

var object = { 'some_value': 'value', 'some_methid': function(){ return 'method result'}}

You can read and set property 'some_value', for example:

object['some_value'] // return 'value'object.some_value // return 'value'

// STEP 2

Ok, in your methods of database.js you pass db variable, but this is not of db instance, it is mongoose model, and you must write like this:

module.exports.findBookByTitle = function (model, title, callback) {    model.findOne({        title: title    }, function (err, doc) {        if (err || !doc) callback(null);        else callback(doc.text);    });};module.exports.findProductsByName = function (model, name, callback) {    model.findOne({        name: name    }, function (err, doc) {        if (err || !doc) callback(null);        else callback(doc.products);    });};

You can only declare module.exports once in a file, so you should change:

In your database.js file:

module.exports.saveBook 

to

exports.saveBook 

and so on

Take a look at this: https://www.sitepoint.com/understanding-module-exports-exports-node-js/

in package.json folder find mongodb inside dependencies and update with these value:

"mongodb": "^2.2.33",

Then Run

npm install

again. That will solve your probem.