Mongoose.js transactions

Question

I know MongoDB doesn\'t support transactions as relational databases do, but I still wonder how to achieve atomicity for several operations. Hunting around the web, I see people

Answer 1

This question is quite old but for anyone who stumbles upon this page, you could use fawn. It's an npm package that solves this exact problem. Disclosure: I wrote it

Say you have two bank accounts, one belongs to John Smith and the other belongs to Broke Individual. You would like to transfer $20 from John Smith to Broke Individual. Assuming all first name and last name pairs are unique, this might look like:

var Fawn = require("fawn");
var task = Fawn.Task()

//assuming "Accounts" is the Accounts collection 
task.update("Accounts", {firstName: "John", lastName: "Smith"}, {$inc: {balance: -20}})
  .update("Accounts", {firstName: "Broke", lastName: "Individual"}, {$inc: {balance: 20}})
  .run()
  .then(function(){
    //update is complete 
  })
  .catch(function(err){
    // Everything has been rolled back. 

    //log the error which caused the failure 
    console.log(err);
  });

Caveat: tasks are currently not isolated(working on that) so, technically, it's possible for two tasks to retrieve and edit the same document just because that's how MongoDB works.

It's really just a generic implementation of the two phase commit example on the tutorial site: https://docs.mongodb.com/manual/tutorial/perform-two-phase-commits/