deep populating in mongoose - mongodb

Question

I've got two schemas,
one for user and another one for post
in the user schema, I've got a property for latestPost which would be an ObjectId of an entry in the post schema
when I load up the user object,
I want to get the lastestPost as an object that includes the author's username from the user schema where the author is an ObjectId that'd match an _id field in the user schema.
the mongoose tutorials seem to use the syntax of
User.findOne({ _id: req.user.id})
.populate('latestPost')
.populate({ path: 'latestPost', populate: 'author'})
but it doesn't work
it's showing
{ _id: 58f54fa51febfa307d02d356,
username: 'test',
email: 'test#test',
firstName: 'test',
lastName: 'test',
__v: 0,
latestPost:
{ _id: 58f54fa51febfa307d02d357,
user: 58f54fa51febfa307d02d356,
author: 58f54fa51febfa307d02d356,
date: 2017-04-17T23:28:37.960Z,
post: 'Test',
__v: 0 } }
but I want it to show
latestPost:
{
author: {
username : something
}
}
how does one do something like this? is there something wrong with the design of the schema or the query?
var UserSchema = new Schema({
username : String,
firstName : String,
lastName : String,
email : String,
password : String,
views : Number,
latestPost : { type: Schema.Types.ObjectId, ref: 'Post' }
});
var PostSchema = new Schema({
user : { type: Schema.Types.ObjectId, ref: 'User' },
author : { type: Schema.Types.ObjectId, ref: 'User' },
date : Date,
body : String
});
var User = mongoose.model('User', UserSchema);
var Post = mongoose.model('Post', PostSchema);
User.findOne({ _id: req.user.id})
.populate('latestPost')
.populate({ path: 'latestPost', populate: 'author'})
.exec(function(err, user) {
if (err) res.json(err)
console.log(user)
})

Answer 1

Maybe just this.
I don't think you need .populate('latestPost') as your next .populate() should take care of populating the latestPost. Maybe that is interfering with the next one.
User.findOne({ _id: req.user.id }).populate({
path: 'latestPost',
model: 'Post',
populate: {
path: 'author',
model: 'User'
}
}).exec(function (err, user) {
});

Answer 2

You need to provide the model name also in populate function:
var UserSchema = new Schema({
username : String,
firstName : String,
lastName : String,
email : String,
password : String,
views : Number,
latestPost : { type: Schema.Types.ObjectId, ref: 'Post' }
});
var PostSchema = new Schema({
user : { type: Schema.Types.ObjectId, ref: 'User' },
author : { type: Schema.Types.ObjectId, ref: 'User' },
date : Date,
body : String
});
var User = mongoose.model('User', UserSchema);
var Post = mongoose.model('Post', PostSchema);
User.findOne({ _id: req.user.id})
.populate('latestPost')
.populate({
model: 'Post',
path: 'latestPost',
select: 'author -_id'
})
.exec(function(err, user) {
if (err) res.json(err)
console.log(user)
})