mongoose model has no access to connections in-progress transactions - mongodb

Question

In my current express application I want to use the new ability of mongodb multi-doc transactions.
First of all it is important to point out how I connect and handle the models
My app.js (server) firstly connects to the db by using db.connect().
I require all models in my db.index file. Since the models will be initiated with the same mongoose reference, I assume that future requires of the models in different routes point to the connected and same connection. Please correct me if I'm wrong with any of these assumptions.
I save the connection reference inside the state object and returning it when needed for my transaction later
./db/index.ts
const fs = require('fs');
const path = require('path');
const mongoose = require('mongoose');
const state = {
connection = null,
}
// require all models
const modelFiles = fs.readdirSync(path.join(__dirname, 'models'));
modelFiles
.filter(fn => fn.endsWith('.js') && fn !== 'index.js')
.forEach(fn => require(path.join(__dirname, 'models', fn)));
const connect = async () => {
state.connection = await mongoose.connect(.....);
return;
}
const get = () => state.connection;
module.exports = {
connect,
get,
}
my model files are containing my required schemas
./db/models/example.model.ts
const mongoose = require('mongoose');
const Schema = mongoose.Schema;
const ExampleSchema = new Schema({...);
const ExampleModel = mongoose.model('Example', ExampleSchema);
module.exports = ExampleModel;
Now the route where I try to do a basic transaction. F
./routes/item.route.ts
const ExampleModel = require('../db/models/example.model');
router.post('/changeQty', async (req,res,next) => {
const connection = db.get().connection;
const session = await connection.startSession(); // works fine
// start a transaction
session.startTransaction(); // also fine
const {someData} = req.body.data;
try{
// jsut looping that data and preparing the promises
let promiseArr = [];
someData.forEach(data => {
// !!! THIS TRHOWS ERROR !!!
let p = ExampleModel.findOneAndUpdate(
{_id : data.id},
{$incr : {qty : data.qty}},
{new : true, runValidators : true}
).session(session).exec();
promiseArr.push(p);
})
// running the promises parallel
await Promise.all(promiseArr);
await session.commitTransaction();
return res.status(..)....;
}catch(err){
await session.abortTransaction();
// MongoError : Given transaction number 1 does not match any in-progress transactions.
return res.status(500).json({err : err});
}finally{
session.endSession();
}
})
But I always get the following error, which probably has to do sth with the connection reference of my models. I assume, that they don't have access to the connection which started the session, so they are not aware of the session.
MongoError: Given transaction number 1 does not match any in-progress
transactions.
Maybe I somehow need to initiate the models inside db.connect with the direct connection reference ?
There is a big mistake somewhere and I hope you can lead me to the correct path. I appreciate Any help, Thanks in advance

Answer 1

This is because you're doing operations in parallel:
So you've got a bunch of race conditions. Just use async/await
and make your life easier.
let p = await ExampleModel.findOneAndUpdate(
{_id : data.id},
{$incr : {qty : data.qty}},
{new : true, runValidators : true}
).session(session).exec();
Reference : https://github.com/Automattic/mongoose/issues/7311
If that does not work try to execute promises one by one rather than promise.all().