MongoError: The positional operator did not find the match needed from the query. at Function.create() - node.js

Question

I am trying to update values into an object array(users) if it does not already exist in MongoDB. Here is my Schema:
ownerid:{
type: Number,
required: 'This field is required'
},
name:{
type: String
},
capacity:{
type: Number
},
basePrice:{
type: Number
},
users:[{
id: Number,
price: Number,
target: Number,
frequency: Number
}],
filePath:{
type: String
},
status:{
type: String
}
});
The following is my router method:
app.post('/userBid',urlEncodedParser,function(req,res){
resName=req.body.resName;
console.log(resName);
Resource.find({"name":resName},{"users.id": userid},function(err,existingUser){
if (!existingUser){
console.log("already in queue");
//res.render('userHome.ejs');
}
else{
console.log("in update");
Resource.update({'name': resName},
{'$set': {
'users.$.frequency': 1,
'users.$.id': userid,
'users.$.price': req.body.price,
'users.$.target': req.body.target
}},{'multi': true},
function(err,model) {
if(err){
console.log(err);
return res.send(err);
}
return res.json(model);
});
}
});
});
I have tried using $push but that does not seem to work either. Also I can't use '0' instead of '$' as multiple users will be inserted by the users and I need to store them all.

Answer 1

Issue :
Reason why we use $ is to update a specific object/few specific objects in an array field that meet our condition. So when you use any positional operators like $ or $[] then in filter part of .update({filterPart},{updatePart}) query you need to use a filter to find specific object in array. So for example if id field is unique in users array then you can use it to filter/find the object needs to be updated.
Try this below code :
app.post("/userBid", urlEncodedParser, function (req, res) {
resName = req.body.resName;
console.log(resName);
/** Use findOne if `name` is unique.
* Cause `existingUser` will be array, instead findOne will return an object or null - So you can just do if(existingUser)to check true values */
Resource.find({ name: resName }, { "users.id": userid }, function (
err,
existingUser
) {
if (!existingUser) {
console.log("already in queue");
//res.render('userHome.ejs');
} else {
console.log("in update");
Resource.update(
{ name: resName, "users.id": userid }, /** `"users.id": userid` is the only change needed */
{
$set: {
"users.$.frequency": 1,
"users.$.id": userid,
"users.$.price": req.body.price,
"users.$.target": req.body.target,
},
},
{ multi: true },
function (err, model) {
if (err) {
console.log(err);
return res.send(err);
}
return res.json(model);
}
);
}
});
});