MongoDB find doesn't return an error if a record doesn't exist?

Question

I'm using Mongoose:

user.find({username: 'xyz'}, function(err, doc){
  if(err){
    res.render('error', {errorMsg: "Error blah blah"})
  }
});

I'm deliberately using a user who doesn't exist xyz and it's not triggering any errors, I thought it was because of Mongoose but then I tried in MongoDB shell and yes MongoDB won't return an error if a record doesn't exist.

>db.accounts.find({username: 'xyz'})
> // no error, blank line

How do I handle that? I want the execution of the script stop if a user doesn't exist.

Yea, that one is from 3 years ago. Things are constantly changing especially with NodeJS. — Vegan Sv
– Vegan Sv, Commented Jun 9, 2016 at 16:34
Sure, but this hasn't changed. A query that doesn't match anything just returns an empty result set (for find), or a null result (for findOne). — JohnnyHK
– JohnnyHK, Commented Jun 9, 2016 at 19:21
There may be new users, new views, new solutions to how this can be handled. — Vegan Sv
– Vegan Sv, Commented Jun 9, 2016 at 22:36

Sede · Accepted Answer · 2016-06-09 16:10:17Z

5

Well, if the "username" doesn't exist, that doesn't mean there is an error. Instead you should do something like this.

user.find({ username: 'xyz' }, function(err, doc){
  if(doc.length === 0 || err){
    res.render('error', { errorMsg: "Error blah blah" } )
  }
});

Or more verbose version:

user.find({ username: 'xyz' }, function(err, doc) {
    if(err){
        res.render('error', { errorMsg: "Error blah blah" } )
    } else {
        if (doc.length === 0) {
            console.log("User doesn't exist");
        } else {
            //do something
        }
    }
});

edited Jun 9, 2016 at 16:10

answered Jun 9, 2016 at 15:53

Sede

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1 Comment

Vegan Sv Over a year ago

Yea I would assume it would trigger an error. Thanks! I havent thought of checking if doc is empty!

inorganik · Accepted Answer · 2016-06-09 15:24:29Z

1

var user = db.accounts.findOne({username: 'xyz'});

if (!user) {
   // handle error
   alert('fail');
}

answered Jun 9, 2016 at 15:24

inorganik

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2 Comments

Vegan Sv Over a year ago

Thanks but I can't think of a way how I can use this. I mean it would kind of work in Mongo shell (there is no alert in either shell or NodeJS) but there should be a callback that returns a result due to asynchronous nature of NodeJS. Even if I don't use Mongoose I'm not sure this is going to work unless it's some sort of a new hack I'm not aware of. Yet yes this is how you would do it in a syncronous environment.

Paul Stelian Over a year ago

@VeganSv If you're in an async function you can omit the callback and you will get a promise. Await it, then check its result.

Joe · Accepted Answer · 2021-03-16 07:07:18Z

0

Try to check if the doc is null or not first and then you can get on with your function.

user.find({ username: 'xyz' }, function(err, doc){
   if(doc === null || err){
      res.render('error', { errorMsg: "Error blah blah" } )
   }
   else {
      do something...
    }
});

answered Mar 16, 2021 at 7:07

Joe

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