unable to populate documents using mongoose populate() - mongodb

Question

I am making an application in express using mongoose. I have a collection called users in which there is a filed called _subscriptions, which is an array of objects and each object contains a field named field which is an ObjectId for the documents of fields (this is another collection in my db).
I want to make such an API which after getting id parameter returns me a user form users collection with field attribute populated instead of its id in value of the field field. For this I am using populate method but it is not working.
This is screenshot showing users collection:
This is screenshot showing fields collection:
This is schema for field (File name Field.js):
var mongoose = require('mongoose');
var Schema = mongoose.Schema;
var FieldSchema = new Schema(
{
_id: Schema.Types.ObjectId,
name: String,
price: Number,
_categories: [{
type: Schema.ObjectId,
}],
}
);
module.exports = mongoose.model('Field', FieldSchema);`
This is schema and model for users
var mongoose = require('mongoose');
var Schema = mongoose.Schema;
var UserSchema = new Schema({
_id: Schema.Types.ObjectId,
salt: String,
provider: String,
name: String,
email: {
type: String,
required: true
},
password: {
type: String,
required: true
},
_subscriptions: [{
field: {
type: mongoose.Schema.ObjectId,
ref: 'Field',
},
status: String,
dateSubscribed: Date,
payments: [{}]
}],
role: String,
});
module.exports = mongoose.model('User', UserSchema);
This is code for user router
var Field = require('../model/Field');
var express = require('express');
var router = express.Router();
var User = require('../model/User');
router.get('/',function(req, res, next) {
User.find({}, function(err, result) {
if (err) {
console.log(err);
res.send('something wrong');
}
res.status(200).send(result);
}).populate( '_subscriptions.field').exec(function (err, story) {
if (err) return handleError(err);
console.log('Here!!!!!');
});
});
router.get('/findById/:id',function(req, res, next) {
var id = req.params.id;
User.findById(id, function(err, doc) {
if (err) {
console.error('error, no entry found');
}
res.status(200).send(doc);
}).populate('field').exec(function (err, story) {
if (err) return handleError(err);
console.log('Here!!!!!');
});
});
router.get('/getSubscriptions/:id',function(req, res, next) {
var id = req.params.id;
User.findById(id, function(err, doc) {
if (err) {
console.error('error, no entry found');
}
var type = typeof(doc);
res.status(200).send(doc);
})
});
module.exports = router;
This is where I have called app.use method:
And this is response I am getting using postman
I am looking forward for someones' assistance in resolving this issue
as i am unable to identify my mistake. Your help in this regard will be highly appreciated.
Thanking in advance

Answer 1

What I have understood is, In the user collection, there is _subscriptions and in _subscriptions, there is field. If this is your schema, then you should pass "_subscriptions.field" as a parameter to the populate function not "field" as you have passed currently.
So, your code for user's sub route, /findById/:id, must be like this:
router.get('/findById/:id',function(req, res, next) {
var id = req.params.id;
User.findById(id, function(err, doc) {
if (err) {
console.error('error, no entry found');
}
res.status(200).send(doc);
}).populate('_subscriptions.field').exec(function (err, story) {
if (err) return handleError(err);
console.log('Here!!!!!');
});
});