Retrieving ID of subdocument after update in MongoDB - node.js

Question

I wrote a service to push a new data to my collection using update statement and I need to retrieve the id of last inserted data. I am using db.collection.update for this, but it just giving a response like this:
{
"result": {
"ok": 1,
"nModified": 1,
"n": 1
}
}
My api for that is:
app.post('/feeds',function(req,res) {
var _id = req.body._id;
var title = req.body.title;
var description = req.body.description;
var latitude = Number(req.body.latitude);
var longitude = Number(req.body.longitude);
db.user.update(
{_id:_id },
{$push : {
feed:{
title: title,
description:description,
latitude:latitude,
longitude:longitude
}
}
},function (err,result) {
if (err) {
res.json({"success": '0', "message": "Error adding data"});
}
else {
res.json({'result':result});
}
});
});
This is my Mongoose schema:
var user = new mongoose.Schema({
username : {type: String},
email : {type: String,index: {unique: true}},
password : {type: String},
feed : [{
title : {type: String},
description : {type: String},
latitude : {type:Number},
longitude : {type:Number},
feedImages : [{
imageUrl: {type: String}
}],
}]
});
I want to add data to feed.
My database structure
I want the id of newly pushed feed.

Answer 1

Embedded way (current schema)
If you want to use one document per feed and pushing sub-documents into (embedded way), you can pre-assign a _id to your newly created feed sub-document:
var feedId = new ObjectId();
db.user.update({
_id: _id
}, {
$push: {
feed: {
_id: feedId,
title: title,
description: description,
latitude: latitude,
longitude: longitude
}
}
}, function(err, result) {
/* ...your code... */
});
Don't forget to add a index for user.feed._id if you want to query for this field (using ensureIndex orcreateIndex depending of your mongodb version).
Using separate collection
As alternative way, you can use a separate feed collection, and use insert statements including a userId foreign key.
You can find more about pro/cons using Multiple Collections vs Embedded Documents here.

Answer 2

You should use db.user.insert() , why do you need the id, when you already have it from the req body?
db.user.insert(objectToInsert, function(err,docsInserted){
console.log(docsInserted);
});

Answer 3

It's a good case for findOneAndUpdate.
Finds a matching document, updates it according to the update arg, passing any options, and returns the found document (if any) to the callback. The query executes immediately if callback is passed.
Available options
new: bool - if true, return the modified document rather than the original. defaults to false (changed in 4.0)