iOS Swift - Local Data Persistence
Why does this Core Data fetch fail?
let fetchRequest = NSFetchRequest(entityName: "Person")
fetchRequest.predicate = NSPredicate(format: "age > %@", 30)
let results = try context.fetch(fetchRequest)
Why does this Core Data fetch fail? let fetchRequest = NSFetchRequest(entityName: "Person") fetchRequest.predicate = NSPredicate(format: "age > %@", 30) let results = try context.fetch(fetchRequest)
medium📝 Debug Q7 of 15
Step-by-Step Solution
Solution:
Step 1: Understand predicate format specifiers
%@ expects an object like NSNumber, but 30 is an Int literal, causing failure.Step 2: Correct usage
Wrap 30 as NSNumber(value: 30) or use %d for Int in predicate format.Final Answer:
Using %@ with an Int instead of NSNumber causes predicate failure -> Option BQuick Check:
Use NSNumber with %@ in predicates [OK]
Quick Trick: Use NSNumber for %@ in NSPredicate format [OK]
Common Mistakes:
- Passing Int directly with %@
- Assuming generic type causes fetch failure
- Misreading predicate format string
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