selecting array element using unique id not working in mongodb - node.js

Question

My application has "Posts" which will have stories
Now I want to select one post and only one of its stories from multiple stories in the story array
var db = req.db;
var mongo = require('mongodb');
var collection = db.get('clnPost');
var userId = req.body.userId;
var postId = req.body.postId;
var storyId = req.body.storyId;
var ObjectID = mongo.ObjectID;
var mongo = require('mongodb');
var ObjectID = mongo.ObjectID;
collection.find({ _id: ObjectId(postId), "Stories._id": ObjectID(req.body.storyId)}, function (e, docs) {
//some processing on the docs
}
I want this to return the post along with only story which has the story Id that is sent through the request, but its returning all the stories in the stories array
Here I am getting all the stories for that post, where as i need only the story with Id that matches req.body.storyId
I also tried using $elemMatch after checking this question but still got the same results
collection.find({ _id: postId}, {Stories: { $elemMatch: { _id: req.body.storyId } } }, function (e, docs) {
I also tried
collection.find({ "Stories._id":ObjectID(storyId)}, {"Stories.$":1,Stories: {$elemMatch: { "Stories._id" :ObjectID(storyId) }} } , function (e, docs) {
The structure of the post document is as follows
{
"_id": {
"$oid": "55a7847ee4b07e03cc6acd21"
},
"Stories": [
{
"userId": "743439369097985",
"story": "some story goes on here",
"_id": {
"$oid": "55c0b9367d1619a81daaefa0"
},
"Views": 29,
"Likes": []
},
{
"userId": "743439369097985",
"story": "some story goes on here",
"_id": {
"$oid": "55c0bbd97abf0b941aafa169"
},
"Views": 23,
"Likes": []
}
]
}
I also tried using $unwind
var test= collection.aggregate( //where collection =db.get('clnPost')
{ $match: { "Stories._id": ObjectID(storyId) } },
{ $project : { Stories : 1 } },
{ $unwind : "$Stories" }
);
Update 1: i am using monk and hence aggregate is not working

Answer 1

I can not copy your example document, so I used similar one:
{
"_id" : "55a7847ee4b07e03cc6acd21",
"Stories" : [{
"userId" : "743439369097985",
"story" : "some story goes on here",
"_id" : "55c0b9367d1619a81daaefa0",
"Views" : 29,
"Likes" : [ ]
}, {
"userId" : "743439369097985",
"story" : "some story goes on here",
"_id" : "55c0bbd97abf0b941aafa169",
"Views" : 23,
"Likes" : [ ]
}]
}
To get what you want, you need to use dollar projection operator in a way I used it here.
db.collection.find({
"Stories._id": "55c0bbd97abf0b941aafa169"
}, {
"Stories.$": 1
}).pretty()