Node.js and mongoose (mongodb) error cannot read property '' of null

Question

I have a findOne query, and when ever i verify if it returned a empty document i get thrown a error saying 'cannot read property 'username' of null'. That happend when i try to acess doc.username in if(!doc.username) {

My code:

function checkAccDb(username, password) { console.log(2);
    /* Check if accounts exists in db */
    db.findOne({username: username}, function(err, doc){ console.log(3);
        if(err) throw err;

        if(!doc.username) {
            add2stack(username, password);
        }
        else if(doc.status == 200) {
            end(username, password, 1000);
        }
        else if(doc.status == 401) {
            if(doc.password == password)
                end(username, password, 401);
            else
                add2stack(username, password);
        }
        else {
            add2stack(username, password);
        }
    });
}

Could anyone please explain me what's happening here?

Thanks!

Answer 1

The query succeeds but doesn't find any matches, so both err and doc are null. You need to check if doc is null and handle that case appropriately.

Answer 2

A typical implementation would be like this

db.findOne({username: username},function(err, doc) {
  if (err) {
    // handle error
  }
  if(doc != null)
  {
    if(!doc.username)
    {
        //handle case
    }
    else
    {
        //handle case
    }
  }
});