fix: add warning that @Attribute(.unique) is not supported with CloudKit #8
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CloudKit cannot enforce unique constraints across devices due to its distributed, asynchronous sync model. Using @Attribute(.unique) with CloudKit sync will cause crashes or be silently ignored. This commit: - Adds a prominent warning in the CloudKit Constraints section - Shows correct pattern (regular property with default) vs incorrect (@Attribute(.unique)) - Provides deduplication strategy for apps that need uniqueness checks
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CloudKit sync cannot enforce SwiftData uniqueness (@Attribute(.unique) / #Unique). Don’t use uniqueness constraints with CloudKit-backed SwiftData stores.
This commit:
@Attribute(.unique)with CloudKit will either:Sources
Sources for CloudKit + @Attribute(.unique) Issue
Stack Overflow
Thread discussing crashes with unique constraints and CloudKit
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Developer reports crash scenarios
FatBobMan (Well-known SwiftData Expert)
*
Comprehensive SwiftData guide stating CloudKit doesn't support unique constraints
DevTechie
Documents that even the iOS 18 #Unique macro is NOT compatible with CloudKit
Firewhale.io
Lists CloudKit data model rules including no unique constraints
Apple Developer Forums
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WWDC23 Lab confirmations about CloudKit constraints applying to SwiftData