I've built a series of database queries in my express app that reside in a /models/index.js file which I can access from app.js via var express = require('express');. I am trying to populate req.session.user with a userid that is returned by a findByEmail(); function in /models/index.js.
The findByEmail(); function works fine, however I can't figure out how to store its return value in req.session. I've tried including req.session.id = result.rows[0].id; in the 'findByEmail();function, but this returns areq is not defined` error.
Am I overlooking a simple require statement in my /models/index.js file or is there another trick to accessing req.session in a module?
I've included the relevant code from /models.index.js below:
/models.index.js:
var pg = require('pg');
function findByEmail(email){
pg.connect(function(err, client, done) {
if(err) {
console.log('pg.connect error');
throw err;
}
client.query('BEGIN', function(err) {
if(err) {
console.log('client.query BEGIN error');
return rollback(client, done);
}
process.nextTick(function() {
var text = "SELECT * FROM users WHERE email = $1";
client.query(text, [email], function(err, result) {
if(err) {
console.log(err);
return rollback(client, done);
}
console.log(result);
console.log(result.rows);
console.log('id: ', result.rows[0].id);
req.session.id = result.rows[0].id;
done();
});
});
});
});
}
module.exports.pg = pg;
exports.findByEmail = findByEmail;
As far as /models/index.js knows, req is not defined, same thing with rollback. A module is a closure and you don't have access to variables defined outside of it.
If you want to do that you must pass them as parameters but it's not very good design, as #gustavohenke said: Separation of concerns.
You might want to have a callback and call it with success/error and set the session id there so you don't have to pass in into the module:
function findByEmail(email,callback){
pg.connect(function(err, client, done) {
if(err) {
console.log('pg.connect error');
throw err;
}
// Do all the async work and when you are done ...
// An error is usually passed as the first parameter of the callback
callback(err,result)
});
}
exports.findByEmail = findByEmail;
You would then call it like this:
var models = require('./models');
models.findByEmail('thedude#lebowski.com',function(err,results) {
// set session id here where you probably have access to the req object...
})
Related
I'm building a mockup website to try and learn NodeJS. I want a login system and I'm trying to connect my register page with my database script. The sql function that sends queries to the database is working as intended, however, when trying to call the query function from the script that manages the register webpage all I get is an error 500.
It would be cool if someone could point me in the right direction, surely it's some quirk from NodeJS I don't know about yet.
Here is my register page script that should call the query function from POST routing:
var express = require('express');
var router = express.Router();
var db = require('../public/javascripts/dbController');
router
.get('/', function(req, res, next) {
res.render('register.html', {title: 'Register'})
})
.post('/', function(req, res, next) {
register(req.body);
res.render('register.html', {title: 'Register'})
})
function register(request)
{
let username = request.login;
let password = request.password;
let sql = "INSERT INTO users (user_username, user_password, user_status) VALUES ('"+username+"','"+password+"', 1);";
console.log("query");
//Why is this not working?
db.query(sql);
}
module.exports = router;
And here is (part of) my dbController script:
const sqlite3 = require('sqlite3').verbose();
let db = new sqlite3.Database('./public/database/db.db', sqlite3.OPEN_READWRITE, (err) => {
if (err && err.code == "SQLITE_CANTOPEN") {
createDatabase();
return;
} else if (err) {
console.log("Getting error " + err);
exit(1);
}
});
//This function is not running when I ask for it in register.js
function query(sql){
console.log("running query: " + sql)
db.all(sql, [], (err, rows) => {
if (err) {
throw err;
}
rows.forEach((row) => {
console.log(row.name);
});
});
}
module.exports = query;
I figure that I probably have to route my scripts through the main app script or maybe I'm exporting wrong? Anyway, any nudge in the right direction would be great because I've been stuck on it a few days. Thanks!
For what I can see, you're indeed importing the "query" function into your "register" page. But you're setting a name of "db" to it.
var db = require('../public/javascripts/dbController');
but you're not exporting "db" you're exporting "query":
module.exports = query;
But that's not really the issue, you could just call it "myRandomNameImport" and it would still work. The problem is that you're accessing a property of "db" that does not exist.
db.query(sql); /* <- db.query does not exist.
* Try db(sql) instead. */
"db" does not have any properties called "query", the function you're trying to use is "db".
function register(request) {
let username = request.login;
let password = request.password;
let sql = "INSERT INTO users (user_username, user_password, user_status) VALUES ('"+username+"','"+password+"', 1);";
console.log("query");
db(sql); /*<- Just call db()*/
}
The code is set up this way:
var express = require('express');
var router = express.Router();
var mongo = require('mongodb').MongoClient;
function getData(){
db.collection("collection_name").find({}).toArray(function (err, docs) {
if (err) throw err;
//doing stuff here
}
var dataset = [
{//doing more stuff here
}
];
});
}
router.get("/renderChart", function(req, res) {
mongo.connect(url_monitor, function (err, db) {
assert.equal(null, err);
getData(res);
});
});
When I run the code and trying to get to /renderChart when running, I get the "ReferenceError: db is not defined". I came across a similar case, and think it may be a similar problem caused because mongodb.connect() is called asynchronously, but I couldn't get it to work:
Express js,mongodb: "ReferenceError: db is not defined" when db is mentioned outside post function
The problem here is you don't pass the db to the function, so it's undefined.
A solution:
function getData(db, res){
db.collection("collection_name").find({}).toArray(function (err, docs) {
if (err) throw err;
//doing stuff here
}
var dataset = [
{//doing more stuff here
}
];
});
}
router.get("/renderChart", function(req, res) {
mongo.connect(url_monitor, function (err, db) {
assert.equal(null, err);
getData(db, res);
});
});
You'll probably need to pass the req at some point too, or make specific db queries. And you'll probably want to use promises or async/await to better deal with all asynchronous calls.
Its Simple Javascript.
You are using a variable db in your file, which is not defined, so it will throw an error.
You need to do something like this .
var findDocuments = function(db, callback) {
// Get the documents collection
var collection = db.collection('documents');
// Find some documents
collection.find({}).toArray(function(err, docs) {
assert.equal(err, null);
assert.equal(2, docs.length);
console.log("Found the following records");
console.dir(docs);
callback(docs);
});
}
I have the same problem before, instead of passing db to routing function, My solution is to make db variable global like
var mongojs = require('mongojs')
global.db = mongojs(<mongodb url>);
then db variable can be used in any part of your code
If you're using express, put that in your app.js file and you will never have to worry about db variable anyore.
PS: some people think that using global is not a good practices, but I argue that since global is a node.js features and especially since it works, why not
node.js global variables?
You don't have tell the codes, that which database you want to use.
how to get databases list https://stackoverflow.com/a/71895254/17576982
here is the sample code to find the movie with name 'Back to the Future' in database sample_mflix > collection movies:
const { MongoClient } = require("mongodb");
// Replace the uri string with your MongoDB deployment's connection string.
const uri =
"mongodb+srv://<user>:<password>#<cluster-url>?retryWrites=true&writeConcern=majority";
const client = new MongoClient(uri);
async function run() {
try {
await client.connect();
const database = client.db('sample_mflix');
const movies = database.collection('movies');
// Query for a movie that has the title 'Back to the Future'
const query = { title: 'Back to the Future' };
const movie = await movies.findOne(query);
console.log(movie);
} finally {
// Ensures that the client will close when you finish/error
await client.close();
}
}
run().catch(console.dir);
to get list of database, put await client.db().admin().listDatabases() on fun function. e.g.
async function run() {
try {
await client.connect();
var databasesList = await client.db().admin().listDatabases();
console.log("Databases:");
databasesList.databases.forEach(db => console.log(` - ${db.name}`));
learn MongoDB more from official docs: https://www.mongodb.com/docs
var database = require('database');
var express = require('express');
var app = express();
var cors = require('cors');
app.use(cors());
var bodyParser = require('body-parser');
var urlencodedParser = bodyParser.urlencoded({
extended: false
});
app.post('/dosomething', urlencodedParser, function(req, res) {
if (!req.body.a) {
res.status(500).send(JSON.stringify({
error: 'a not defined'
}));
return;
}
firstAsyncFunction(req.body.a, function(err, result) {
if (err) {
res.status(500).send('firstAsyncFunction was NOT a success!');
} else {
if (result.b) {
secondAsyncFunction(result.b, function(err, data) {
if (err) {
res.status(500).send('secondAsyncFunction was NOT a success!');
return;
}
res.send('EVERYTHING WAS A SUCCESS! ' + data);
});
}
else {
res.status(500).send('result.b is not defined');
}
}
});
});
function firstAsyncFunction(param, callback) {
//Some network call:
// Return either return (callback(null,'success')); or return (callback('error'));
var query = database.createQuery(someOptionsHere);
database.runDatabaseQuery(query, function(err, entities, info) {
if (err) {
return (callback('error'));
}
return (callback(null, 'success'));
});
};
function secondAsyncFunction(param, callback) {
//Some network call:
// Return either return (callback(null,'success')); or return (callback('error'));
var query = database.createQuery(someOptionsHere);
database.runDatabaseQuery(query, function(err, entities, info) {
if (err) {
return (callback('error'));
}
return (callback(null, 'success'));
});
};
var server = app.listen(process.env.PORT || 3000, function() {
var host = server.address().address;
var port = server.address().port;
console.log('App listening at http://%s:%s', host, port);
});
module.exports = app;
I have here a basic express http server. This server has one route, dosomething, which makes two network calls and tells the user if they were a success or not.
This is my entire webserver (this is a bare bones server of my actual server for example purposes). I am now concerned with this server crashing. Reading the docs for express I see there is a default error handler which will catch errors and prevent the server from crashing (http://expressjs.com/en/guide/error-handling.html). I have added the code:
function defaultErrorHandler(err, req, res, next) {
if (res.headersSent) {
return next(err);
}
res.status(500);
res.render('error', { error: err });
}
app.use(defaultErrorHandler);
This still crashes my server though. For example. I had a problem with my database returning an improper JSON response and inside of my firstAsyncFunction (not shown in the code) I tried to parse the JSON and it caused an error telling me it was improper JSON and the server crashed and was unable to take requests anymore until I restarted it. I would like to avoid this and have the default error handler send out a generic response back to the user when this occurs. I thought if I specified the defaultErrorHandler and put it inside of app.use that it would capture and handle all errors, but this does not seem to be the case? Inside of my async function for example you can see I am looking if an error was returned and if it was I send an error back to the user, but what if some other error occurs, how can I get express to capture and handle this error for me?
The defaultErrorHandler cannot handle exceptions that are thrown inside asynchronous tasks, such as callbacks.
If you define a route like:
app.get('/a', function(req, res) {
throw new Error('Test');
});
An error will be thrown, and in this case defaultErrorHandler will successfully catch it.
If the same exception occurs in an async manner, like so:
app.get('/a', function(req, res) {
setTimeout(function () {
throw new Error('Test');
}, 1000);
});
The server will crush, because the callback is actually in another context, and exceptions thrown by it will now be caught by the original catcher. This is a very difficult issue to deal with when it comes to callback.
There is more than one solution though. A possible solution will be to wrap every function that is prone to throw error with a try catch statement. This is a bit excessive though.
For example:
app.get('/a', function(req, res) {
setTimeout(function () {
try {
var x = JSON.parse('{');
}
catch (err) {
res.send(err.message);
}
}, 1000);
});
A nicer solution:
A nicer solution, would be to use promises instead, if it's possible, then for example you can declare a single errorHandler function like so:
function errorHandler(error, res) {
res.send(error.message);
}
Then, let's say you have to following function with fetches stuff from the database (I used setTimeout to simulate async behavior):
function getStuffFromDb() {
return new Promise(function (resolve, reject) {
setTimeout(function () {
resolve("{");
}, 100);
});
}
Notice that this function returns an invalid JSON string. Your route will look something like:
app.get('/a', function(req, res) {
getStuffFromDb()
.then(handleStuffFromDb)
.catch(function (error) { errorHandler(error, res) });
});
function handleStuffFromDb(str) {
return JSON.parse(str);
}
This is a very simplified example, but you can add a lot more functionality to it, and (at least theoretically) have a single catch statement which will prevent your server from crushing.
I have a simple file model.js like follows:
var mongo = require('mongodb');
var mongoUri = process.env.MONGOLAB_URI ||
process.env.MONGOHQ_URL ||
'mongodb://localhost/mydb';
exports.connect = mongo.Db.connect(mongoUri, function(err, db) {
console.log("Connect to the database successfully")
});
and in my web.js I load the model using model = require('./model.js'). One werid thing is that although I did not call model.connect(), the message "Connect to the database successfully" still got logged to my console. Why is this happening and is there a way to avoid it?
EDIT:Never mind I have found a workaround:
exports.connect = function(){
mongo.Db.connect(mongoUri, function(err, db) {
console.log("Connect to the database successfully")
});
}
exports.connect = mongo.Db.connect(mongoUri, function(err, db) {
console.log("Connect to the database successfully")
});
You just called mongo.Db.connect() and assigned its result to exports.connect.
That code runs as soon as you require() the module.
Instead, you need to create a function:
exports.connect = function() { ... };
I've got two node.js files: server.js and database.js. I want my socket.io emitting to happen in server.js and the database queries in database.js. Server.js:
// init
io.sockets.on('connection', function(socket) {
initdb = db.initdb();
console.log(initdb)
});
My database.js contains basically the following code:
function query(queryString) {
connection = mysql.createConnection({
host: '12.23.45.67',
user: 'user',
password: 'password',
database: 'database'
});
connection.connect();
var res = connection.query(queryString, function(err, rows, fields) {
if (err) throw err;
});
connection.end();
}
// export initdb for external usage by server.js
exports.initdb = function() {
var initdb = query("SELECT * FROM columns;");
};
My problem is that I want the rows object from within the connection.query function to be returned to my initdb function. However the only place where I can log this object is within that function. How can I pass the query results so I can emit the JSON object it from server.js?
Remember that node is asynchronous. So for the most part, you get data back through callbacks rather than as return values to functions.
You'll need to chain a callback through to where your query happens, something like:
// in database.js
exports.initdb = function(cb) {
query("SELECT * FROM columns", cb)
}
function query(queryString, cb) {
// .. stuff omitted
var res = connection.query(queryString, function(err, rows, fields) {
connection.end();
if (err) return cb(err);
cb(null,rows);
});
// in server.js
io.sockets.on('connection', function(socket) {
db.initdb(function(err,rows) {
if (err) {
// do something with the error
} else {
console.log(rows)
}
});
});
The callback would be a function taking 2 parameters, err and rows. Your server.js code would need to check the value of err and act accordingly, otherwise it would have the rows.