Mongoose- How to use discriminators in subdocument - node.js

Question

I want the output to be like this
var FeedSchema = new Schema({
timestamp : {type : String, required : true},
feed_type_code : {type : Number, required : true},
gender : {type : String, required : true},
feed_item : Article || Tip || etc.
}
Hence, I understand I have to use discriminators. I followed the following SO answer
Here is what I did:
var feed_type = {discriminatorKey : 'feed_item'};
var FeedSchema = new Schema({
timestamp : {type : String, required : true},
feed_type_code : {type : Number, required : true},
gender : {type : String, required : true}
}, feed_type);
var TipSchema = new Schema({
tip : {type : String, required : true},
subtip : {type : String, required : true},
display_count : {type : Number},
likes : {type : Number}
}, feed_type);
var ArticleSchema = new Schema({
title : {type : String, required : true},
english_title : {type : String, required : true},
image_url : {type : String, required : true},
article_text : {type : String, required : true},
english_article_text : {type : String},
author : {type : String},
english_author : {type : String}
}, feed_type);
Here is how I am saving the document:
var article = new Article({
title : req.body.title,
english_title : req.body.english_title,
image_url : req.body.image_url,
article_text : req.body.article_text,
english_article_text : req.body.english_article_text,
author : req.body.author,
english_author : req.body.english_author
});
var feed = new Feed({
gender : req.body.gender,
timestamp : moment().valueOf(),
feed_type_code : 9002,
feed_item : article
});
feed.save(function(err, doc){
if(err){
res.json({success : -1});
return;
}
res.json({success : 1, feed : doc});
});
I am not getting the article output for this:
{
"success": 1,
"feed": {
"__v": 0,
"gender": "female",
"timestamp": "1481460218959",
"feed_type_code": 9002,
"_id": "584d49faa6ff3a23bc868ab3"
}
}
I am new to Nodejs. I would appreciate if you can point out the error.

Answer 1

in the model file add these lines
var Feed = mongoose.model('Feed', FeedSchema, 'feed');
var Article = Feed.discriminator('Article', ArticleSchema);
var Tip = Feed.discriminator('Tip', TipSchema);
module.exports = {
Feed : Feed,
Article : Article,
Tip : Tip
}
This is how you save the document. You don't need to create a separate Feed object.
var article = new Article({
gender : req.body.gender,
timestamp : moment().valueOf(),
feed_type_code : 9002,
title : req.body.title,
english_title : req.body.english_title,
image_url : req.body.image_url,
article_text : req.body.article_text,
english_article_text : req.body.english_article_text,
author : req.body.author,
english_author : req.body.english_author
});
article.save(function(err, doc){
if(err){
console.log(err);
res.json({success : -1});
return;
}
res.json({success : 1, feed : doc});
});