Mongoose - accessing nested object with .populate - node.js

Question

Schema Definitions
Team.js
var TeamSchema = new Schema({
// Team Name.
name: String,
lead: String,
students :type: [{
block : Number,
status : String,
student : {
type: Schema.ObjectId,
ref: 'Student'
}]
});
Student.js
var StudentSchema = new Schema({
name: String,
rollNo : Number,
class : Number
});
How I can populate "student" to get output, as below:
team
{
"__v": 1,
"_id": "5252875356f64d6d28000001",
"students": [
{
"__v": 1,
"_id": "5252875a56f64d6d28000002",
block : 1,
status : joined,
"student": {
"name": Sumeeth
"rollNo" : 2
"class" : 5
}
},
{
"__v": 1,
"_id": "5252875a56f64d6d28000003",
block : 1,
status : joined,
"student": {
"name": Sabari
"rollNo" : 3
"class" : 4
}
}
],
"lead": "Ratha",
}
This is JS I use to get the document using Mongoose:
Team.findOne({
_id: req.team._id
})
.populate('students')
.select('students')
.exec(function(err, team) {
console.log(team);
var options = {
path: 'students.student',
model: 'Student'
};
Student.populate(team.students,options,function(err, students) {
console.log(students);
if (err) {
console.log(students);
res.send(500, {
message: 'Unable to query the team!'
});
} else {
res.send(200, students);
}
});
});
In my console output I get the following:
{ _id: 53aa434858f760900b3f2246,
students
[ { block : 1
status: 'joined'
_id: 53aa436b58f760900b3f2249 },
{ block : 1
status: 'joined'
_id: 53aa436b58f760900b3f2250 }]
}
And the expected output is:
{ _id: 53aa434858f760900b3f2246,
students
[ { block : 1
status: 'joined'
student :{
"name": Sumeeth
"rollNo" : 2
"class" : 5
}
},
{ block : 1
status: 'joined'
student :{
"name": Sabari
"rollNo" : 3
"class" : 4
}
}
]
}
Some one please help me where I am wrong. How should I make use of .populate, so that , I can get the entire student object and not only its id.
Reference :
Populate nested array in mongoose

Answer 1

I have been facing same issue. I have use this code for my rescue :
Team.findOne({_id: req.team._id})
.populate({ path: "students.student"})
.exec(function(err, team) {
console.log(team);
});

Answer 2

Here is a simplified version of what you want.
Basic data to set up, first the "students":
{
"_id" : ObjectId("53aa90c83ad07196636e175f"),
"name" : "Bill",
"rollNo" : 1,
"class" : 12
},
{
"_id" : ObjectId("53aa90e93ad07196636e1761"),
"name" : "Ted",
"rollNo" : 2,
"class" : 12
}
And then the "teams" collection:
{
"_id" : ObjectId("53aa91b63ad07196636e1762"),
"name" : "team1",
"lead" : "me",
"students" : [
{
"block" : 1,
"status" : "Y",
"student" : ObjectId("53aa90c83ad07196636e175f")
},
{
"block" : 2,
"status" : "N",
"student" : ObjectId("53aa90e93ad07196636e1761")
}
]
}
This is how you do it:
var async = require('async'),
mongoose = require('mongoose');
Schema = mongoose.Schema;
mongoose.connect('mongodb://localhost/team');
var teamSchema = new Schema({
name: String,
lead: String,
students: [{
block: Number,
status: String,
student: {
type: Schema.ObjectId, ref: 'Student'
}
}]
});
var studentSchema = new Schema({
name: String,
rollNo: Number,
class: Number
});
var Team = mongoose.model( "Team", teamSchema );
var Student = mongoose.model( "Student", studentSchema );
Team.findById("53aa91b63ad07196636e1762")
.select('students')
.exec(function(err, team) {
console.log( team );
async.forEach(team.students, function(student,callback) {
Student.populate(
student,
{ "path": "student" },
function(err,output) {
if (err) throw err;
callback();
}
);
},function(err) {
console.log( JSON.stringify( team, undefined, 4 ) );
});
});
And it gives you the results:
{
"_id": "53aa91b63ad07196636e1762",
"students": [
{
"block": 1,
"status": "Y",
"student": {
"_id": "53aa90c83ad07196636e175f",
"name": "Bill",
"rollNo": 1,
"class": 12
}
},
{
"block": 2,
"status": "N",
"student": {
"_id": "53aa90e93ad07196636e1761",
"name": "Ted",
"rollNo": 2,
"class": 12
}
}
]
}
You really do not need the "async" module, but I am just "in the habit" as it were. It doesn't "block" so therefore I consider it better.
So as you can see, you initial .populate() call does not do anything as it expects to "key" off of an _id value in the foreign collection from an array input which this "strictly speaking" is not so as the "key" is on "student" containing the "foreign key".
I really did cover this in a recent answer here, maybe not exactly specific to your situation. It seems that your search did not turn up the correct "same answer" ( though not exactly ) for you to draw reference from.

Answer 3

You are overthinking it. Let Mongoose do the work for you.
Team.findOne({
_id: req.team._id
})
.populate({path:'students'})
.exec(function(err, team) {
console.log(team);
});
This will return students as documents rather than just the ids.

Answer 4

TL DR
const team = await Team.findById(req.team._id)
.populate("students");
team.students = await Student.populate(team.students, {path: "student"});
Context
Reading from all the answers I went testing everything and just Neil Lun's answer worked for me. The problem is it was on the path to a cb hell. So I cracked my head a little and 'refactored' to an elegant one-liner.
const foundPost = await Post.findById(req.params.id)
.populate("comments")
.populate("author");
foundPost.comments = await User.populate(foundPost.comments, {path: "author"});
My initial problem:
{
title: "Hello World",
description: "lorem",
author: {/* populated */},
comments: [ // populated
{text: "hi", author: {/* not populated */ }}
]
};
How my models basically are:
User = {
author,
password
};
Post = {
title,
description,
author: {}, //ref User
comments: [] // ref Comment
};
Comment = {
text,
author: {} // ref User
};
The output after problem solved:
{
comments: [
{
_id: "5dfe3dada7f3570b60dd977f",
text: "hi",
author: {_id: "5df2f84d4d9fcb228cd1df42", username: "jo", password: "123"}
}
],
_id: "5da3cfff50cf094c68aa2a37",
title: "Hello World",
description: "lorem",
author: {
_id: "5df2f84d4d9fcb228cd1aef6",
username: "la",
password: "abc"
}
};