Why is some data lost when getting data from mongodb?

Question

JavaScript

The function of adding photos and comments, it works well and everything appears in the database, but
loadDatabase.js

The code:

var mongoose = require('mongoose');
mongoose.connect('mongodb://localhost/cs142project6');

//        ....

var allPromises = Promise.all(userPromises).then(function () {
        var photoModels = [];
        var userIDs = Object.keys(mapFakeId2RealId);
        for (var i = 0; i < userIDs.length; i++) {
            photoModels = photoModels.concat(cs142models.photoOfUserModel(userIDs[i]));
        }
        var photoPromises = photoModels.map(function (photo) {
            return Photo.create({
                file_name: photo.file_name,
                date_time: photo.date_time,
                user_id: mapFakeId2RealId[photo.user_id]
            }, function (err, photoObj) {
                if (err) {
                    console.error('Error create user', err);
                } else {

                    photo.objectID = photoObj._id;
                    if (photo.comments) {
                        photo.comments.forEach(function (comment) {
                            photoObj.comments.push({
                                comment: comment.comment,
                                date_time: comment.date_time,
                                user_id: comment.user.objectID
                            });
                            console.log("Adding comment of length %d by user %s to photo %s",
                                comment.comment.length,
                                comment.user.objectID,
                                photo.file_name);
                        });
                    }
                    photoObj.save();
                    console.log('Adding photo:', photo.file_name, ' of user ID ', photoObj.user_id);
                    
                }
            });
        });

Result:

When you receive comments on the photo disappear. I can't find where the error is.
webServer.js

The code:

var mongoose = require('mongoose');
var async = require('async');
mongoose.connect('mongodb://localhost/cs142project6');

//         ....

app.get('/photosOfUser/:id', function (request, response) {
       if (!request.session ||!request.session.login_name) {
        response.status(401).send();
        return;
    }
    var user_id = request.params.id;
    Photo.find({user_id: user_id}, function (err, photos) {
        if (photos === undefined) {
           response.status(400).send('Bad param ' + user_id);
            return;
        }
        if (err) {
            console.error('Doing /photosOfUser/' + user_id + 'error:', err);
            response.status(400).send(JSON.stringify(err));
            return;
        }

        var Photo = JSON.parse(JSON.stringify(photos));
        async.each(Photo, function (photo, doneCallback) {
            
        
            delete photo.__v;
            async.each(photo.comments, function (comment, comment_callback) {
                var temp_user_id = comment.user_id;
                console.log("user id "+temp_user_id);
                delete comment.user_id;
               User.findOne({user_id: temp_user_id}, function(err, user) {
                    if (err) {
                        comment_callback(err);
                        return;
                    }
                    if (user.length === 0) {
                        response.status(400).send('Missing user id');
                        return;
                    }
                    comment.user = JSON.parse(JSON.stringify(user));
                    console.log("user "+user);
                    delete comment.user.occupation;
                    delete comment.user.description;
                    delete comment.user.location;
                    delete comment.user.__v;
                    delete comment.user.password;
                    delete comment.user.login_name;
                   delete comment.user.salt;
                   delete comment.user.password_digest;

                    comment_callback();
                });
            }, function (err) {
                doneCallback(err);
            });
        }, function (err) {
            if (err) {
                response.status(400).send(JSON.stringify(err));
            }
            response.end(JSON.stringify(Photo));
        });
    });
});

Result:

Answer 1

Because coments comes in an array, parse the array and you'll be happy.