How to handle persistent state multiplayer games on iOS (+PHP/mySql)
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**Proposed Situation:**<br />
Imagine an iPhone game: A farm, comprised of 100 plantable crop squares. Each crop square has two possible states (EMPTY or PLANTED). The farm object (*100 crop squares*) is stored in a mySql table as a json string object. We expose a php web service for retrieving/updating the farm.


**Question:**<br />
Have you been down this road before? What are some good approaches for managing the 'farm object' so that multiple users can be updating / retrieving the same farm simultaneously from their respective iPhones, without any conficts? Will I need to start from scratch and re-invent the wheel (subversion?) or is there already some appropriate code out there?