nodejs-demo

Transaction solution

In this solution, we just handler transaction at collection tier. We create a clone of collections before write and revert all related collections when an exception has thrown.

We call Transaction.start(collections, process, callback) to run a process which contains many update database actions. Once method has called, we lock all collections that defined in collections, and other actions which want to update database have to wait (Need to check write permission before run!).

Before run process, we create backups of collections, then call proccess. After process ran completely, if no exception has thrown, we clean backup collections and unlock database.

Install and run

install dependencies:

    $ cd nodejs-demo && npm install

run the app:

    $ DEBUG=app:* npm start

Open http://localhost:3000 to view demo screen.

run test:

    $ DEBUG=app:* npm test

How to use?

Take a look at lib/like.js, We define a process function, it will receive DB instance and a promise instance. And process contains all update-database actions. In any case of error, we just throw it out and Transaction will revert to previous version of collections.

var Transaction = require('./transaction');

exports = module.exports;

exports.save = function (data, callback) {
  data.productId = parseInt(data.productId);
  function process (DB, promise) {
    return promise.then(function () {
      if (data.hasOwnProperty('makeException')) {
        throw Error('Some exception when insert new like');
      }
      return DB.getCollection('likes').insertOne(/*data*/);
    }).then(function () {
      return DB.getCollection('products').update(/*data*/)
    });
  }
  return Transaction.start(['products', 'likes'], process, callback);
}