Okay, so in the past few days I started messing with Node (because I think I should learn something that is actually useful and might get me a job). Right now, I know how to serve pages, basic routing and such. Nice. But I want to learn how to query databases for information.
Right now, I'm trying to build an app that serves as a webcomic website. So, in theory, the application should query the database when I type in the url http://localhost:3000/comic/<comicid>
I have the following code in my app.js file:
router.get('/', function(req, res) {
var name = getName();
console.log(name); // this prints "undefined"
res.render('index', {
title: name,
year: date.getFullYear()
});
});
function getName(){
db.test.find({name: "Renato"}, function(err, objs){
var returnable_name;
if (objs.length == 1)
{
returnable_name = objs[0].name;
console.log(returnable_name); // this prints "Renato", as it should
return returnable_name;
}
});
}
With this setup I get console.log(getName()) to output "undefined" in the console, but I have no idea why it doesnt get the only element that the query can actually find in the database.
I have tried searching in SO and even for examples in Google, but no success.
How the hell am I supposed to get the parameter name from the object?
NodeJs is async. You need a callback or Promise.
router.get('/', function(req, res) {
var name = '';
getName(function(data){
name = data;
console.log(name);
res.render('index', {
title: name,
year: date.getFullYear()
});
});
});
function getName(callback){
db.test.find({name: "Renato"}, function(err, objs){
var returnable_name;
if (objs.length == 1)
{
returnable_name = objs[0].name;
console.log(returnable_name); // this prints "Renato", as it should
callback(returnable_name);
}
});
}
The getName function is making an asynchronous call to Mongo with db.test.find. You can see this by adding a console.log after the async function. Like this:
function getName(){
db.test.find({name: "Renato"}, function(err, objs){
var returnable_name;
if (objs.length == 1) {
returnable_name = objs[0].name;
console.log(returnable_name);
return returnable_name;
}
});
console.log('test'); // <!-- Here
}
In all likeliness, this will output:
test
Renato
You need to provide a callback to your getName function.
router.get('/', function(req, res) {
getName(function(err, name) {
res.render('index', {
title: name,
year: date.getFullYear()
});
})'
});
function getName(cb){
db.test.find({name: "Renato"}, function(err, objs){
if(err) cb(err);
var returnable_name;
if (objs.length == 1) {
returnable_name = objs[0].name;
return cb(null, returnable_name);
} else {
// Not sure what you want to do if there are no results
}
});
}
Related
I am currently developing a website with an API that I built with node.js, express and MongoDb for the database.
I am curretly learning node and express and cant find my way to create a middleware to verify that the USER ID matches the POSTED BY ID from a COMMENT. That way the USER can only delete his own comments.
My middleware looks like this
verifyUserIdPostedBy.js
const Comment = require('../models/Comment');
var userId
var postedById
module.exports = {
verfyUserIdPostedBy: function (req, res, next) {
userId = req.header('userId')
postedById = Comment.findOne({ _id: req.params.commentId}).populate('postedBy') .exec( function (error, body) {
if (error) throw new Error(error);
req.postedById = body.postedBy._id // assign the ID to the req object
console.log(req.postedById);
});
console.log(userId);
if(userId !== req.postedById)
return res.status(500).json({message: 'Stopped'})
return next();
},
}
My console.log() in the middleware show me exactly the 2 values that I want to compare but I get the error 'Stopped' and my verification never happens. I tried accesing the route with the comment owner and also with not the comment owner and none works
and my route looks like this
comments.js
const express = require('express');
const router = express.Router();
const Comment = require('../models/Comment');
const verify = require('./verifyToken');
const {verfyUserIdPostedBy} = require('./verfyUserIdPostedBy')
// DELETE COMMENT
router.delete('/:commentId', verify, verfyUserIdPostedBy, async (req, res) => {
try {
const removedComment = await Comment.deleteOne({ _id: req.params.commentId });
res.json(removedComment);
} catch(err){
res.json({message:err});
}
})
Like I said I am new at this but cant find a way to do it properly.
Appretiate in advance any help and advice.
Mario
I add comments in your code to explain how it works :
verfyUserIdPostedBy: function (req, res, next) {
userId = req.header('userId')
postedById = Comment.findOne({ _id: req.params.commentId}).populate('postedBy') .exec( function (error, body) {
/* -----this is a callback function------ */
/* the code inside the callback function is executed only when findOne finish and **after** the code outside */
if (error) throw new Error(error);
req.postedById = body.postedBy._id // assign the ID to the req object
console.log(req.postedById);
});
/* this code is executed before the code inside the callback function */
console.log(req.postedById); // undefined, you can check
console.log(userId);
if(userId !== req.postedById) // this is always true
return res.status(500).json({message: 'Stopped'}) // and this line always executes
return next(); // and this line never execute
},
The concept is callback. I strongly advise you to research this keyword, callback is used massively in NodeJS. Nowadays, there are Promise and async/await that allow developers to write asynchronous code in a "synchronous way", but callback is the base.
In order for your code works, 1 simple solution (there are many solutions!) is put comparison code into the callback block, something like :
const Comment = require('../models/Comment');
var userId
var postedById
module.exports = {
verfyUserIdPostedBy: function (req, res, next) {
userId = req.header('userId')
postedById = Comment.findOne({ _id: req.params.commentId}).populate('postedBy') .exec( function (error, body) {
if (error) throw new Error(error);
req.postedById = body.postedBy._id // assign the ID to the req object
console.log(req.postedById);
console.log(userId);
if(userId !== req.postedById)
return res.status(500).json({message: 'Stopped'})
return next();
});
},
}
postRegistrationHandler: function (account, req, res, next) {
console.log('postRegistrationHandler activated');
account.getCustomData(function(err, data) {
if (err) {
console.log(err.toString, "error string");
return next(err);
} else {
data.mongo_id = userCreationCtrl(account);
data.save();
next();
}
});
},
This function almost works properly, but the line:
data.save();
runs before the previous line finishes which means that the data I want to save isn't present at the appropriate time.
data.mongo_id = userCreationCtrl(account);
This line calls a function that creates a mongoDB document with information in the account object and then returns the _id (which is what I am trying to save.
I thought maybe using a .then() would help but that seems to be unavailable here for some reason. If anyone sees something I'm missing, that would be quite helpful. Thank you!
Here is the userCreationCtrl file as requested:
var UserSchema = require('./../models/UserModel.js');
var createNewUser = function (account, res, next){
// We will return mongoId after it is created by submitting a newUser
var mongoId = "";
// Save StormpathID (last 22 characters of account.href property)
var newStormpathId = account.href.slice(account.href.length - 22);
console.log('stormpath ID:', newStormpathId, 'just registered!');
console.log(account);
// Create new user from model by recycling info from the Stormpath registration form and include the stormpathId as well.
var newUser = new UserSchema({
stormpathId: newStormpathId,
firstName: account.givenName,
lastName: account.surname,
email: account.email,
street: account.street,
city: account.city,
zip: account.zip
});
// This saves the user we just created in MongoDB
newUser.save(function(err, result){
console.log(result);
if (err) {
console.error(err);
}
else {
console.log("User created in MongoDB, attempting to return mongoDB _id to stormpath customData");
// Keep track of the new user's mongo _id so we can return it to the previous function and save it as Stormpath custom data.
mongoId = result._id;
console.log(mongoId, "mongoid");
return result._id;
}
});
};
module.exports = createNewUser;
You have userCreationCtrl expecting 3 arguments, account, res, and next. next is the callback that should be called after the user is created so instead of return result._id you should call next like so:
// inside of createNewUser()
newUser.save(function(err, result){
console.log(result);
if (err) {
console.error(err);
}
else {
console.log("User created in MongoDB, attempting to return mongoDB _id to stormpath customData");
// Keep track of the new user's mongo _id so we can return it to the previous function and save it as Stormpath custom data.
mongoId = result._id;
console.log(mongoId, "mongoid");
// IMPORTANT change to make it all work...
// get rid of return result._id because its not doing anything
// pass the value to your callback function instead of returning the value
next(null, result._id);
}
});
then calling code in postRegistrationHandler should look like this:
account.getCustomData(function(err, data) {
if (err) {
console.log(err.toString, "error string");
return next(err);
} else {
// pass in a callback as the 3rd parameter that will be called by newUser.save() when its finished
userCreationCtrl(account, null, function(err, resultId) {
data.save();
next();
});
}
});
I'm using Express and Handlebars to display a value set by the user and stored in the database.
Handlebars is set up to display the value "{{userMotto}}".
Express does the following:
function isUserAuthenticated(req, res, next) {
if (!req.user) {
res.render('index', {
user: req.user
});
} else {
currentUser = req.user.username;
userMottoCaught = queryDatabase("motto", currentUser);
next();
}
}
I want it to set the value of "userMottoCaught" to whatever it finds in the database. The query itself is this:
function queryDatabase(dbCollection, dbUID) {
this.dbCollection = dbCollection;
this.dbUID = dbUID;
return MongoClient.connectAsync(hiddenkeys.mongodbUri)
.then(function(db) {
return db.collection(dbCollection).findOneAsync({
_id: dbUID
});
})
.then(function(item) {
console.log("Found: ");
console.log(item);
return dbQueryResult;
})
.catch(function(err) {
//err
});
}
The problem is that I cannot for the life of me get the dbQueryResult out and return it to function queryDatabase itself. Probably because it's being returned to a sub function right now instead of the main function, I think. I highly suspect this can be easily resolved but I'm just at a loss on how to fix this. I am using Bluebird here to see if I could solve this with promises, but I'm not sure this is the right route either. I've also looked into callbacks but I cannot for the life of me figure out how to apply either concept to my code to solve my problem.
Later on when I render the page I do this to render it on the page:
router.get('/', isUserAuthenticated, function(req, res) {
res.render('dashboard', {
user: req.user,
userMotto: userMottoCaught
});
});
Currently this yields on the page: "Motto: [object Promise]", because I haven't returned the proper value to the main function.
Is there anyone out there with some wise words?
Cheers,
Dean
i think you need to make a callback here
function isUserAuthenticated(req, res, next) {
if (!req.user) {
res.render('index', {
user: req.user
});
} else {
currentUser = req.user.username;
userMottoCaught = queryDatabase("motto", currentUser,function(err,data){
userMottoCaught = data
next();
});
}
}
and the definition of queryDatabase should look like
function queryDatabase(dbCollection, dbUID,cb) {
this.dbCollection = dbCollection;
this.dbUID = dbUID;
return MongoClient.connectAsync(hiddenkeys.mongodbUri)
.then(function(db) {
return db.collection(dbCollection).findOneAsync({
_id: dbUID
});
})
.then(function(item) {
console.log("Found: ");
console.log(item);
dbQueryResult = JSON.stringify(item.motto);
cb(null,dbQueryResult)
})
.catch(function(err) {
//err
cb(err);
});
}
I need to return the search results from Mongoose.findOne to variable
results = Lang.findOne({page: params.page,lang: params.lang, param: params.param}, function(err, lang) {
if( err || !lang) {
console.log("No translation!");
} else {
return lang.trans;
};
}
Is there a way to do this? I tried several hours to find a solution with async. functions and nothing ...
I also found articles where it was said that this is impossible, but is there any alternative for realize this?
It's really important to me because I need this to my multilingual project, I need to get the translation:
res.render('index',{titleGen : req.__({page:'home', lang:req.locale, param:'hello'})});
Here is the solution:
exports.getLang = getLang = function(params,callback){
console.log('received: '+params.page+' + '+params.lang+' + '+params.param);
Lang.findOne({page: params.page, lang: params.lang, param: params.param},function(err, lang){
if(err)
console.log(err)
else{
callback(lang.trans);
}
});
}
and routing:
router.get('/', function(req, res) {
req.__({page:'home', lang:req.locale, param:'hello'},function(text){
res.render('index',{titleGen : text });
})
});
I'm learning node.js so bear with me.
I'm trying to create a node.js web application using express+jade that is basically just a line queue. (I.E. take a number, wait in line, now serving number 4...except the 4 will be a mysql table field). The page will auto-update every 5 seconds. There are three line queues handled by the page (I.E) :3000/1 :3000/2 :3000/3.
To be clear, I have the application working, but I want to make sure I am doing it correctly as opposed to just hacking it together with poor methodology.
In my index.js I have the standard setup:
exports.bio = function(req, res){
res.render('index', {
location: 'Biometrics',
number: bio()
});
};
exports.interview = function(req, res){
res.render('index', {
location: 'Interview',
number: interview()
});
};
exports.docs = function(req, res){
res.render('index', {
location: 'Documentation',
number: doc()
});
};
I am currently also calling the values for the "number:" JSON value from within the index.js as well.
var doc = (function() {
//do javascript and data calls
return a;
});
var bio = (function() {
//do javascript and data calls
return a;
});
var interview = (function() {
//do javascript and data calls
return a;
});
My question is: What would be the recommended way to do this or am I on the right track?
This will work as long as the functions doc(), bio(), and interview() are synchronous, but most likely that won't be the case, particularly if they need to perform some database access.
If these functions were async then your could should look like this:
exports.docs = function(req, res){
// call the doc() function and render the response in the callback
doc(function(err, number) {
res.render('index', {
location: 'Documentation',
number: number
});
});
};
The doc() function will look like this:
var doc = (function(callback) {
// This code very likely be async
// therefore it won't return any value via "return"
// but rather calling your function (callback)
db.doSomething(someparams, callback);
});
Inside db.doSomething() there will be a call to your function callback(err, theValue)
The asynchonous way would be something like:
exports.docs = function(req, res) {
fetchSomeValueFromMysql(req.param('foo'), function (err, data) {
if (err) {
res.send(500, 'boom!');
return;
}
res.render('index', {
location: 'Documentation',
number: data
});
});
};
Say if you had an async operation in bio();
exports.bio = function (req, res) {
bio(function (err, data) {
if (!err && data) {
res.render('index', {
location: 'Biometrics',
number: data
});
} else {
// handle error or no data
res.render('error');
}
});
}
var bio = function(cb) {
//do javascript and data calls
cb(err, data);
});
Again, there are many ways to get this working. But the above should do.