I’ve been venturing into the world of MongoDB via Mongoid in a Rails app. On one hand it’s a breath of fresh air (no migrations, flexible schemas etc.) but on the other hand I really, really miss transactions.
If somebody asked me if I used transactions much in MySQL, I would probably have said no… however, now that I don’t have them I realise just how much I used them. Things that just work when using ActiveRecord such as creating a record and ensuring that an associated record gets created is sooo much harder.
MongoDB has “Atomic Operations” which means if you have an embedded relationship, all is good and the database will be rolled back if the entire document does not save. As soon as you have two top level collections and need to ensure that a record is created in both, things get a little hairy.
There seems to be a great deal of “if you need transactions just use a RDBMS” talk but what if you need a flexible schema and transactions, the last thing you want to manage is some kind of EAV system like Magento.
I’ve created a thread on the Mongo User forum with a typical example so feel free to join in the discussion. I’d love to hear experienced Mongo user’s views on how to overcome these kinds of situations and what kind of applications people are running with MongoDB.