Node and Mongodb connection problems

Question

A few days ago I’m having a problem with a code that I’m having trouble solving. What I’m trying to do at the moment is to register users in mongodb through Node. I am using the view ejs mechanism, but so far I have checked everything and it is correct, the only problem is in the implementation of the function that opens the connection to the Mongodb bank. I am using the standard MVC, follows below the codes.

dbConnection.js file that connects to the database (so far everything seems to be ok):

/* importar o mongodb */
var mongo = require('mongodb');

var connMongoDB = function(){
    console.log('Entrou na função de conexão');
    var db = new mongo.Db(
        'crud',
        new mongo.Server('localhost',
            27017,
            {}
        ),
        {}
    );

    return db;
};

module.exports = function(){
    return connMongoDB;
};

Route register.js (seems to be ok tbm):

module.exports = function(application, res, res){
application.get('/cadastro', function(req, res){
    application.app.controllers.cadastro.cadastro(application, req, res);
});

application.post('/cadastrar', function(req, res){
    application.app.controllers.cadastro.cadastrar(application, req, res);
});
};

Register Controller(Until then I still did the test by passing a console.log of the data variableForm and was returning the data entered in the form normally) :

module.exports.cadastro = function(application, req, res){
res.render('cadastro', {validacao: {}, dadosForm: {}});
};

module.exports.cadastrar = function(application, req, res){

var dadosForm = req.body;

req.assert('nome', 'Nome não pode ser vazio').notEmpty();
req.assert('usuario', 'Usuário não pode ser vazio').notEmpty();
req.assert('senha', 'Senha não pode ser vazio').notEmpty();

var erros = req.validationErrors();

if(erros){
    res.render('cadastro', {validacao: erros, dadosForm: dadosForm});
    return;
};

var connection = application.config.dbConnection; // retorna a variável connMongoDb
var UsuariosDAO = new application.app.models.UsuariosDAO(connection); // passa a variável connMongoDb acima como parâmetro

UsuariosDAO.inserirUsuario(dadosForm);

res.send('Cadastrado com sucesso!');
};

User file. The error starts at line 6 of the code:

function UsuariosDAO(connection){
this._connection = connection(); // recebe a variável db do arquivo dbConnection
};

UsuariosDAO.prototype.inserirUsuario = function(usuario){
this._connection.open( function(err, mongoclient){
    mongoclient.collection("users", function(err, collection){
       collection.insert(usuario);


    });
});
};

module.exports = function(){
return UsuariosDAO;
};

For better view of the problem, follow error code:

TypeError: this._connection.open is not a function
at UsuariosDAO.inserirUsuario (c:\Users\micha\GitHub\Projetos-Praticos\Projeto-CRUD\app\models\UsuariosDAO.js:6:22)
at Object.module.exports.cadastrar (c:\Users\micha\GitHub\Projetos-Praticos\Projeto-CRUD\app\controllers\cadastro.js:23:17)
at c:\Users\micha\GitHub\Projetos-Praticos\Projeto-CRUD\app\routes\cadastro:7:46
at Layer.handle [as handle_request] (c:\Users\micha\GitHub\Projetos-Praticos\Projeto-CRUD\node_modules\express\lib\router\layer.js:95:5)
at next (c:\Users\micha\GitHub\Projetos-Praticos\Projeto-CRUD\node_modules\express\lib\router\route.js:137:13)
at Route.dispatch (c:\Users\micha\GitHub\Projetos-Praticos\Projeto-CRUD\node_modules\express\lib\router\route.js:112:3)
at Layer.handle [as handle_request] (c:\Users\micha\GitHub\Projetos-Praticos\Projeto-CRUD\node_modules\express\lib\router\layer.js:95:5)
at c:\Users\micha\GitHub\Projetos-Praticos\Projeto-CRUD\node_modules\express\lib\router\index.js:281:22
at Function.process_params (c:\Users\micha\GitHub\Projetos-Praticos\Projeto-CRUD\node_modules\express\lib\router\index.js:335:12)
at next (c:\Users\micha\GitHub\Projetos-Praticos\Projeto-CRUD\node_modules\express\lib\router\index.js:275:10)

I hope I have been able to explain the problem correctly. I would be very grateful!