mongodb query with javascript, cursor methods - node.js

Question

I am just creating a simple user login for using MongoDB, Backbone and Node with Express.
I am stuck on querying the database for the user credentials and reliably identifying whether they exist or not.
I'm trying two things here:
// When user posts to the url
app.post('/save/user', function (req, res) {
// create user object and store email from form
var user = {
email : req.body.email
};
// in my collection users
db.collection('users', function (err, collection) {
// create a variable existence with the value, in lamens terms 'yes it does' or 'no it doesnt'
var existence = findOne(collection, {
$query : {email : user.email}
});
});
};
// findOne function passing the collection and the query object
function findOne(coll, query) {
var cursor = coll.find(query).limit(1);
return cursor.hasNext() ? cursor.next() : null;
}
So this is the first way I've been trying. Thing is, I don't understand why the cursor doesn't have 'next(), hasNext(), findOne(), forEach()' and other methods for javascript environment but only for mongo shell.
My question is, how do I access these methods from in my Node.js app?
The second way I tried it :
// When user posts to the url
app.post('/save/user', function (req, res) {
// create user object and store email from form
var user = {
email : req.body.email
};
// in my collection users
db.collection('users', function (err, collection) {
// Have a look for the email entered
var query = collection.find({
$query : {email : user.email}
}).limit(1);
// If it's true, then send response
query.each( function (err, item) {
// If the item does exists, then send back message and don't insert. Otherwise, insert.
if(item !== null) {
console.log('Item does not equal null : ', item);
res.send('The email : ' + item.email + ' already exists');
} else {
console.log('Item does equal null : ', item);
collection.insert(user);
res.send('New user with email : ' + user.email + ' was saved');
}
});
});
};
The problem with this is, it's always going to return null at some point and so I am going to warn the user 'it already exists' and then the next time will be null so it's going to save the email.
I think i'm missing the point so a point in the right direction would be great.
Many thanks in advance!
Well i've looked into a solution but still must be missing the point.
I'm doing an insert, passing in my user object with safe : true but although multiple user objects can be entered, it's still only looking for identical ID;s. I've tried creating an id with new ObjectID() but I still don't understand if a user enters their email adress, thenattempts to create a new user with the same email, it would create a new id for that entry.
By doing the findOne, I can see if it exists easily, Idon't see how it can be done with insert.
app.post('/register/user', function (req, res) {
// Store user details in object
var user = {
username : req.body.user,
email : req.body.email,
password : req.body.password
};
db.collection('users', function (err, collection) {
collection.insert(user, {safe : true}, function (err, doc) {
console.log('what is doc : ', doc);
if(!err) {
res.writeHead(200, {
"Content-Type" : "text/plain",
"Message" : "New user added",
"Access-Control-Allow-Origin" : "*"
});
} else {
console.log('Error is : ', err);
res.writeHead(200, {
"Content-Type" : "text/plain",
"Message" : "User already exists",
"Access-Control-Allow-Origin" : "*"
});
}
res.end();
});
});
});

Answer 1

If you're using the Native Node.JS MongoDB driver, there is a collection.findOne() method and cursors do have nextObject() and each() methods equivalent to the shell methods hasNext() and forEach(). The implementation/naming of the mongo shell equivalents can vary slightly between drivers but you should be able to translate mongo shell examples into Node.JS.
As far as saving a new user goes .. instead of querying for the user before inserting, you would be better to add a unique index on the email field and insert into the collection with safe:true. You can then handle the err result if the insert fails due to a duplicate email. If you do a query before insert there is a potential race condition where the email might not exist when you check for it, but does exist by the time you do the insert.