Uniqueness validation is prone to race conditions.

I'm not really sure what can be done about this, since any fix would likely be at the adaptor level. We currently see uniqueness violations when two model instances with an identical (asserted unique) field are _created_ very close together (i.e. close enough that the uniqueness has been tested for both before the first new instance is created). For example, if you create two new users with the same (should be unique) username at the same time, then they will succeed.

The issue describes a race condition in uniqueness validation across multiple database adapters. Start by examining the validation logic in the ORM's core and the adapter-specific implementations for transactions or locking. Look at how unique constraints are enforced at the database level versus the application level. Testing will require simulating concurrent creation requests.

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