MongoDB - Handle error event - node.js

Question

I have a custom validation when I upload an image to mongoDb. The original name should be unique. If it passes the validation, the code runs properly. But if it fails, it produces error. It says that custom validators that take 2 arguments) are deprecated in mongoose >= 4.9.0. Is there another way to validate the uniqueness of the originalname? Or a way to catch the error? Please help.
router.post('/upload',function(req,res){
Item.schema.path('originalname').validate(function(value, done) {
Item.findOne({originalname: value}, function(err, name) {
if (err) return done(false);
if (name) return done(false);
done(true);
});
});
upload(req,res,function(err, file) {
if(err){
throw err;
}
else{
var path = req.file.path;
var originalname = req.file.originalname;
var username = req.body.username;
var newItem = new Item({
username: username,
path: path,
originalname: originalname
});
Item.createItem(newItem, function(err, item){
if(err) throw err;
console.log(item);
});
console.error('saved img to mongo');
req.flash('success_msg', 'File uploaded');
res.redirect('/users/welcome');
}
});
});
model
var ItemSchema = mongoose.Schema({
username: {
type: String,
index: true
},
path: {
type: String
},
originalname: {
type: String
}
});
var Item = module.exports = mongoose.model('Item',ItemSchema);
module.exports.createItem = function(newItem, callback){
newItem.save(callback);
}

Answer 1

you can provide uniqueness to that field like :-
var ItemSchema = mongoose.Schema({
username: {
type: String,
index: true
},
path: {
type: String
},
originalname: {
type: String,
unique:true // this string will be unique all over the database
}
});
var Item = module.exports = mongoose.model('Item',ItemSchema);
module.exports.createItem = function(newItem, callback){
newItem.save(callback);
}

Answer 2

To validate uniqueness before saving to db, you can try to findOne with tour filename:
router.post('/upload',function(req,res){
Item.findOne({originalname: req.file.originalname}, function(err, name) {
if (err) return done(false); // errors
if (name) return done(false); // check for existence of item here
done(true);
});
});
If findOne function did not respond with any data, it means that, there is no document in collection with the same original name, and you can proceed with adding document to collection