Mongoose Query Population with GridFile Schema

attachment.model.js

const mongoose = require('mongoose')
const schema = require('gridfile')

module.exports = mongoose.model('Attachment', schema, 'attachment.files')

attachment.pdf

email.model.js

const mongoose = require('mongoose')
const { Schema } = mongoose

const schema = new Schema({
  to: {
    type: String,
    required: true
  },
  subject: {
    type: String,
    required: true
  },
  html: {
    type: String,
    required: true
  },
  attachments: [{
    type: Schema.Types.ObjectId,
    ref: 'Attachment'
  }]
})

module.exports = mongoose.model('Email', schema)

index.js

const mongoose = require('mongoose')
const { MongoMemoryServer } = require('mongodb-memory-server')
const fs = require('fs')
const path = require('path')

const Email = require('./email.model')
const Attachment = require('./attachment.model')

const start = async () => {
  // connect to a mongo database
  const mongodb = new MongoMemoryServer()
  const connectionUri = await mongodb.getUri()
  await mongoose.connect(
    connectionUri, { useNewUrlParser: true, useUnifiedTopology: true }
  )

  // upload an attachment from a local file
  const fileStream = fs.createReadStream(path.join(__dirname, 'attachment.pdf'))
  const attachment = new Attachment()
  attachment.filename = 'attachment.pdf'
  const uploadedAttachment = await attachment.upload(fileStream)

  console.log(uploadedAttachment)
  /*
    {
      aliases: [],
      _id: 5f3e8f06a37b5c4b1934a070,
      length: 7945,
      chunkSize: 261120,
      uploadDate: 2020-08-20T14:56:06.925Z,
      filename: 'attachment.pdf',
      md5: 'fa7d7e650b2cec68f302b31ba28235d8'
    }
  */

  // create a new email and link the uploaded attachment
  const email = new Email()
  email.to = 'abskmj@gmail.com'
  email.subject = 'Test Mail'
  email.html = 'Testing ...'
  email.attachments.push(uploadedAttachment)
  const savedEmail = await email.save()

  // find an email and linked attachments
  const foundEmail = await Email.findById(savedEmail).populate('attachments')
  const foundAttachment = foundEmail.attachments[0]

  // download file and save it locally
  const downloadStream = fs.createWriteStream(path.join(__dirname, 'download.pdf'))
  await foundAttachment.download(downloadStream)

  // close mongo connection
  await mongoose.connection.close()
  await mongodb.stop()
}

start()

package.json

{
  "name": "gridfile-email-attachments",
  "version": "1.0.0",
  "description": "",
  "main": "index.js",
  "scripts": {
    "test": "echo \"Error: no test specified\" && exit 1",
    "start": "node ."
  },
  "author": "abskmj@gmail.com",
  "license": "MIT",
  "devDependencies": {
    "standard": "^14.3.4"
  },
  "dependencies": {
    "gridfile": "^1.0.1",
    "mongodb-memory-server": "^6.8.0",
    "mongoose": "^5.10.7"
  }
}