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Comment by mustardo | Hacker News Reader

On the surface it sounds like you might have a case for Mongo, lookout for scenarios like...

* Trading in game items between two users (needs multi document atomic locks if you don't want duplicate or lost items) assuming your "schema" is a document per user

* You want to rename or restructure an attribute in the future, with no schema it's not possible change migrate data easily without writing ad hoc code (maybe you can use third party tools) or changing queries to expect data in multiple "schemas" which quickly gets painful

Good Luck!

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> You want to rename or restructure an attribute in the future, with no schema it's not possible change migrate data easily without writing ad hoc code (maybe you can use third party tools) or changing queries to expect data in multiple "schemas" which quickly gets painful

You can have schemas with MongoDB. There are various libraries to facilitate database design by schema specification.

Also renaming or restructuring your data is not necessarily an easy task with SQL. The nature of a database dictates that how good it works for your application depends on up to how well thought-out your schema is. Having to change your schema around is tasking. One of the reported advantages of document stores when they were becoming trendy was that it was easy to change your schema since your schema is essentially determined and regulated at the application layer.

Also MongoDB has ACIDic transactions now (freaking finally) so if it’s as-advertised then I feel like half of your argument is not really a strong one any more.

If you need a schema, then go with an RDBMS.

Yes players can sell items to other players, so that's the one place so far I've needed to worry about atomicity, but even mongodb docs give examples with how to deal with something like that: https://docs.mongodb.com/manual/tutorial/perform-two-phase-c...

So yes, it's annoying for a very small % of what I'm doing, but 99% of my updates/writes are within a single document, so I find it very nice for development.

About the first use case, well it turns out MongoDB just introduced multi-document transactions today.

If only someone had posted that information to HN

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