/** Setting up storage using multer-gridfs-storage */
    var storage = GridFsStorage({
        gfs : gfs,
        filename: function (req, file, cb) {
            var datetimestamp = Date.now();
            cb(null, file.fieldname + '-' + datetimestamp + '.' + file.originalname.split('.')[file.originalname.split('.').length -1]);
        },
        /** With gridfs we can store aditional meta-data along with the file */
        metadata: function(req, file, cb) {
            cb(null, { originalname: file.originalname });
        },
        root: 'ctFiles' //root name for collection to store files into
    });

    var upload = multer({ //multer settings for single upload
        storage: storage
    }).single('file');

    /** API path that will upload the files */
    app.post('/upload', function(req, res) {
        upload(req,res,function(err){
            if(err){
                 res.json({error_code:1,err_desc:err});
                 return;
            }
            console.log(res.file);
            console.log(res[0].file);
             res.json({error_code:0,err_desc:null});
        });
    });

var UserSchema = new Schema({
    name: String,
    email: {
        type: String,
        lowercase: true
    },
    filepath: String,
});

{
        "_id" : ObjectId("58fb894111387b23a0bf2ccc"),
        "filename" : "file-1492879681306.PNG",
        "contentType" : "image/png",
        "length" : 67794,
        "chunkSize" : 261120,
        "uploadDate" : ISODate("2017-04-22T16:48:01.350Z"),
        "aliases" : null,
        "metadata" : {
                "originalname" : "Front.PNG"
        },
        "md5" : "404787a5534d0479bd55b2793f2a74b5"
}

{

        "name" :"asdf",
        "email" : "asdf@gmail.com",
        "filepath":"file/file-1492879681306.PNG"

    }

{
    "_id" : ObjectId("58fb894111387b23a0bf2ccc"),
    "filename" : "file-1492879681306.PNG",
    "contentType" : "image/png",
    "length" : 67794,
    "chunkSize" : 261120,
    "uploadDate" : ISODate("2017-04-22T16:48:01.350Z"),
    "aliases" : null,
    "metadata" : {
        "originalname" : "Front.PNG",
        "name" :"asdf",
        "email" : "asdf@gmail.com",
        "filepath":"file/file-1492879681306.PNG"
    },
    "md5" : "404787a5534d0479bd55b2793f2a74b5"
}

....
/** With gridfs we can store aditional meta-data along with the file */
metadata: function(req, file, cb) {
    var metadata = {
        originalname: file.originalname,
        // get this information somehow
        name :"asdf",
        email : "asdf@gmail.com",
        filepath:"file/file-1492879681306.PNG"
    };
    cb(null, metadata);
},
....

const mongodb = require('mongodb');
const GridFSBucket = mongodb.GridFSBucket;
const MongoClient = mongodb.MongoClient;

MongoClient.connect('mongodb://yourhost:27017/database').then((db) => {
    const bucket = new GridFSBucket(db, {bucketName: 'ctFiles'});

    bucket
        .find({metadata: {'email' : 'asdf@gmail.com'}})
        .toArray()
        .then((fileInfoArr) => {
            console.log(fileInfoArr);
        });
});

var UserSchema = new Schema({
     name: String,
     email: {
         type: String,
         lowercase: true
     },
     filepath: String,
     fileId: Schema.Types.ObjectId
});

UserModel.findOne({'email' : 'asdf@gmail.com'}, function (err, user) {
    // deal with error
    // store and get the db object somehow

    const bucket = new GridFSBucket(db, {bucketName: 'ctFiles'});

    // A download stream reads the file from GridFs
    const readStream = bucket.openDownloadStream(user.fileId));

    readStream.pipe(/* some writable stream */);
});