mongoose populate not populating an array - node.js

Question

I am facing an issue where mongoose query is not populating an array type.
Here is institute schema
'use strict';
var mongoose = require('mongoose');
var Schema = mongoose.Schema;
var InstituteSchema = new Schema({
name: String,
address: String,
city: String,
country: String,
zip: String,
owner: { type: mongoose.Schema.ObjectId, ref: 'User' },
teachers: [{type: mongoose.Schema.ObjectId, ref: 'Teacher'}],
categories: [String],
created : { type : Date, default : Date.now }
});
module.exports = mongoose.model('Institute', InstituteSchema);
And here is teacher Schema
'use strict';
var mongoose = require('mongoose');
var Schema = mongoose.Schema;
var TeacherSchema = new Schema({
education: [{degree: String, instituteName: String}],
dob: Date,
photoUrl: String,
phoneNumber: String,
owner: {type: mongoose.Schema.ObjectId, ref: 'User'},
institutes: [{type: mongoose.Schema.ObjectId, ref: 'Institute'}],
subjects: [{type: mongoose.Schema.ObjectId, ref: 'Subject'}],
created : { type : Date, default : Date.now }
})
module.exports = mongoose.model('Teacher', TeacherSchema);
Here is a method which queries the institute by owner id
exports.mine = function (req, res, next) {
var ObjectId = mongoose.Types.ObjectId;
var userId = new ObjectId(req.user._id);
Institute.find({
owner: userId
}).populate('teachers').exec(function (err, institute) {
if (err) return next(err);
if (!institute) return res.json(401);
res.json(institute);
});
};
I can see from the db that institute has teacher added
db.institutes.find();
{
"_id" : ObjectId("554719a9f5be11c6d4369264"),
"owner" : ObjectId("5547199bf5be11c6d4369263"),
"country" : "USA",
"name" : "Raghvendra Singh",
"address" : "38589 Royal Ann Cmn",
"city" : "Fremont",
"zip" : "94536",
"created" : ISODate("2015-05-04T07:03:05.569Z"),
"categories" : [ "IIT", "Medical" ],
"teachers" : [ ObjectId("55471965f5be11c6d436925f") ],
"__v" : 3
}
But somehow the query method doesn't populate the teachers collection. The weird thing is that i don't even get the collection with object ids and it returns and institute with empty teacher array.
And when i remove the .populate('teachers') from the method call it indeed returns the teacher array with object ids.
I looked at the documentation and i can't see what am i doing wrong.

Answer 1

First you need to change your Model slightly as mention for teachers feild.
teachers: [ { teacher: { type: Schema.ObjectId, ref: "Teacher" } } ]
exports.mine = function (req, res, next) {
var ObjectId = mongoose.Types.ObjectId;
var userId = new ObjectId(req.user._id);
Institute.find({
owner: userId
}).populate('**teachers.teacher**').exec(function (err, institute) {
if (err) return next(err);
if (!institute) return res.json(401);
res.json(institute);
});
};
Then, change your populate parameter to teachers.teacher . It will work