Save current User into field within array in Mongoose - arrays

Question

Here is a relevant part of my Schema, where I'll make reservations to a "space":
var spaceSchema = new mongoose.Schema({
spaceName: String,
scheduledDates: [{
scheduledDates: String,
author: {
id: {
type: mongoose.Schema.Types.ObjectId,
ref: 'User'
},
username: String
}
}]
});
Author should be the current user that's logged in. Here is my route to update those fields:
router.put('/:space_id/schedule', function(req, res) {
Space.findByIdAndUpdate(req.params.space_id, {
'$push': { 'scheduledDates': req.body.space, 'author': req.user._id }
}, { "new": true, "upsert": true }, function(err, space) {
if (err) {
console.log(err);
} else {
console.log(req.body.space);
}
});
});
I can't access "author" correctly, because it's inside the array. What can I do to update this array, adding a new date and user to make the reservation?
Thank you
UPDATE
I tried to use "_id" instead of "id" in my property but got the same result. It seems like it's ignoring the "author" field, and only saving "scheduledDates"
So the schema was like this:
scheduledDates: [{
scheduledDates: String,
author: {
_id: {
type: mongoose.Schema.Types.ObjectId,
ref: 'User'
},
username: String
}
}]
And then in my route, I changed what I was 'pushing':
'$push': { 'scheduledDates': req.body.space, 'author._id': req.user._id }
UPDATED 2
Changed the way I was getting the object to push:
'$push': {
'scheduledDates': {
'scheduledDates': req.body.space,
'author': { _id: req.user._id, username: req.user.username }
}
}
Now I'm getting the following error:
message: 'Cast to string failed for value "{ scheduledDates: \'04/11/2017\' }" at path "scheduledDates"',
name: 'CastError',
stringValue: '"{ scheduledDates: \'04/11/2017\' }"',
kind: 'string',
value: [Object],
path: 'scheduledDates',
reason: undefined } } }