Connecting to MongoDB

June 24th, 2020 By Alex Hu

Creating the MongoDB is simple enough through MongoDB Altas in the cloud, which can be easily access using MongoDB Compass for viewing the database records.

Create the schema with Mongoose is also easy and the generated models can be used for the CRUD functions.

Maintaining a stable connection to MongoDB Atlas is a bit of a challenge. I tried to make a connection once at the top of the resolver, but once in a while, I will get this error when trying to perform a database operation like find / save / delete:

MongoError: topology was destroyed

I ended up putting my dbConnect() before each resolver operation to reconnecting to the database and retry the connection if necessary,

async deleteArticle(_parent: any, args: any, _context: any, _info: any) {
    await dbConnect()
    await Article.findByIdAndDelete(args.input.id)
    return true
},

The dbConnect() will make a connection and retry up to 10 times if failed.

// dbConnecdt.js
import mongoose from 'mongoose'

const RETRY_MAX = 10
let connected = false

async function dbConnect() {
  if (!connected) {
    let retry = 0
    console.log('dbConnect -> entering, connected = ' + connected)
    while (!connected && retry < RETRY_MAX) {
      try {
        mongoose.Promise = Promise
        await mongoose.connect(process.env.MONGO_URI as string, {
          useNewUrlParser: true,
          useUnifiedTopology: true,
          useFindAndModify: true,
        })
        const connection = mongoose.connection
        connection.on('error', console.error.bind(console, 'dbConnect() connection error:'))
        connected = true
        break
      }
      catch (error) {
        console.error('dbConnect -> retry = ' + retry + ', error', error)
        retry--
      }
    }
    console.log('dbConnect -> exiting dbConnect, connected = ' + connected + ', retry = ' + retry)
  }
}

export default dbConnect