Populate nested array in mongoose - Node.js - node.js

Question

These are my schemas (Topic is parent and contains a list of 'Thought's):
var TopicSchema = new mongoose.Schema({
title: { type: String, unique: true },
category: String,
thoughts: [ThoughtSchema]
}, {
timestamps: true,
toObject: {virtuals: true},
toJSON: {virtuals: true}
});
var ThoughtSchema = new mongoose.Schema({
text: String,
author: {type: mongoose.Schema.Types.ObjectId, ref: 'User'},
votes:[{
_id:false,
voter: {type: mongoose.Schema.Types.ObjectId, ref: 'User'},
up: Boolean,
date: {type: Date, default: Date.now}
}]
}, {
timestamps: true,
toObject: {virtuals: true},
toJSON: {virtuals: true}
});
....
I am trying to read the thought's author and change my get Topic api like this:
...
var cursor = Topic.find(query).populate({
path: 'thoughts',
populate: {
path: 'author',
model: 'User'
}
}).sort({popularity : -1, date: -1});
return cursor.exec()
.then(respondWithResult(res))
.catch(handleError(res));
...
But the author is null.. i also do not get any error in the console. What is wrong here?
Edit: Actually i do not need the Thought as a schema, it does not have its own collection in database. It will be saved in topics. But in order to use timestamps option with thoughts, i needed to extract its contents to a new local schema ThoughtSchema. But i have now defined the contents of thoughtSchema directly in the thoughts array of topics, it still does not work.
Edit2: This is the cursor object just before it is executed. Unfortunately i cannot debug in Webstorm, this is a screenshot from node inspector:

Answer 1

Did you try using Model.populate?
Topic.find(query).populate('thoughts')
.sort({popularity : -1, date: -1})
.exec(function(err, docs) {
// Multiple population per level
if(err) return callback(err);
Thought.populate(docs, {
path: 'thoughts.author',
model: 'User'
},
function(err, populatedDocs) {
if(err) return callback(err);
console.log(populatedDocs);
});
});
UPDATE:
You can try with deep populate like this:
Topic.find(query).populate({
path: 'thoughts',
populate: {
path: 'author',
model: 'User'
}
})
.sort({popularity : -1, date: -1})
.exec(function(err, docs) {
if(err) return callback(err);
console.log(docs);
});

Answer 2

How about
Topic.find(query).populate('thoughts')
.sort({popularity : -1, date: -1})
.exec(function(err, docs) {
// Multiple population per level
if(err) return callback(err);
Topic.populate(docs, {
path: 'thoughts.author',
model: 'User'
},
function(err, populatedDocs) {
if(err) return callback(err);
console.log(populatedDocs);
});
});

Answer 3

These are the schemas :
var TopicSchema = new mongoose.Schema({
title: { type: String, unique: true },
category: String,
thoughts: [ThoughtSchema]
}, {
timestamps: true,
toObject: {virtuals: true},
toJSON: {virtuals: true}
});
var ThoughtSchema = new mongoose.Schema({
text: String,
author: {type: mongoose.Schema.Types.ObjectId, ref: 'User'},
votes:[{
_id:false,
voter: {type: mongoose.Schema.Types.ObjectId, ref: 'User'},
up: Boolean,
date: {type: Date, default: Date.now}
}]
}, {
timestamps: true,
toObject: {virtuals: true},
toJSON: {virtuals: true}
});
Did you try Aggregation Instead of Populate. Aggregate Makes much easier for populating the embedded data using $lookup. Try the below code.
UPDATE
Topic.aggregate([{$unwind: "$thoughts"},{ $lookup: {from: 'users', localField: 'thoughts.author', foreignField: '_id', as: 'thoughts.author'}},{$sort:{{popularity : -1, date: -1}}}],function(err,topics){
console.log(topics) // `topics` is a cursor.
// Perform Other operations here.
})
Explanation:
$unwind: Deconstructs an array field from the input documents to output a document for each element.
$lookup: The $lookup stage does an equality match between a field from the input documents with a field from the documents of the “joined” collection. The lookup does the population's job.
$lookup works like
from : this says from which collection the data needs to be populated.(users in this scenario).
localField : this is the local field which needs to be populated. (thoughts.author in this scenario).
foreignField : this is the foreign field present in the collection from which data needs to be populated (_id field in users collection in this scenario).
as : this is the field as what you want to display the joined value as. (this will project thoughts.author's id as thoughts.author document).
Hope this works.