从Coredata中删除一个对象（出错）

Question

我尝试从coredata中删除一个与Test2匹配的对象。我试过这个：

let context = self.fetchedResultsController.managedObjectContext 
    let fetchRequest = NSFetchRequest(entityName:"Person") 
    fetchRequest.predicate = NSPredicate(format: "name = Test2") 
    var error : NSError? 
    let results = managedObjectContext!.executeFetchRequest(fetchRequest, error:&error) 

    context.deleteObject(results.firstObject as NSManagedObject) 

我在这行代码中得到一个错误：context.deleteObject(results.firstObject as NSManagedObject)。它说：Cannot invoke 'deleteObject' with an argument list of type '(NSManagedObject)'。有人知道我能如何解决这个错误吗？

UPDATE：

2015-07-12 20:43:09.601 Note[4222:138125] *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: 'Unable to generate SQL for predicate (name == Test2) (problem on RHS)' 
*** First throw call stack: 
(
0 CoreFoundation      0x000000010ebd6c65 __exceptionPreprocess + 165 
1 libobjc.A.dylib      0x0000000110741bb7 objc_exception_throw + 45 
2 CoreData       0x000000010e7f0bbc -[NSSQLGenerator newSQLStatementForRequest:ignoreInheritance:countOnly:nestingLevel:] + 1724 
3 CoreData       0x000000010e7dcdc4 -[NSSQLAdapter _statementForFetchRequest:ignoreInheritance:countOnly:nestingLevel:] + 244 
4 CoreData       0x000000010e6f4e0c -[NSSQLAdapter _newSelectStatementWithFetchRequest:ignoreInheritance:] + 316 
5 CoreData       0x000000010e6f4a86 -[NSSQLCore newRowsForFetchPlan:] + 118 
6 CoreData       0x000000010e6f433c -[NSSQLCore objectsForFetchRequest:inContext:] + 524 
7 CoreData       0x000000010e6f3dbb -[NSSQLCore executeRequest:withContext:error:] + 299 
8 CoreData       0x000000010e7cea6c __65-[NSPersistentStoreCoordinator executeRequest:withContext:error:]_block_invoke + 3356 
9 CoreData       0x000000010e7d7c30 gutsOfBlockToNSPersistentStoreCoordinatorPerform + 192 
10 libdispatch.dylib     0x0000000111e65614 _dispatch_client_callout + 8 
11 libdispatch.dylib     0x0000000111e4b002 _dispatch_barrier_sync_f_invoke + 365 
12 CoreData       0x000000010e7c9245 _perform + 197 
13 CoreData       0x000000010e6f3a58 -[NSPersistentStoreCoordinator executeRequest:withContext:error:] + 504 
14 CoreData       0x000000010e6f22ca -[NSManagedObjectContext executeFetchRequest:error:] + 586 
15 Note        0x000000010e4efb72 _TFC5Note14ViewController19deleteSelectedTasksfS0_FT_T_ + 738 
16 Note        0x000000010e4ef843 _TFC5Note14ViewController7delTaskfS0_FT_T_ + 51 
17 Note        0x000000010e4ef882 _TToFC5Note14ViewController7delTaskfS0_FT_T_ + 34 
18 Foundation       0x000000010f011744 __NSFireTimer + 83 
19 CoreFoundation      0x000000010eb3e174 __CFRUNLOOP_IS_CALLING_OUT_TO_A_TIMER_CALLBACK_FUNCTION__ + 20 
20 CoreFoundation      0x000000010eb3dd35 __CFRunLoopDoTimer + 1045 
21 CoreFoundation      0x000000010eaffd3d __CFRunLoopRun + 1901 
22 CoreFoundation      0x000000010eaff366 CFRunLoopRunSpecific + 470 
23 GraphicsServices     0x000000011128ca3e GSEventRunModal + 161 
24 UIKit        0x000000010f475900 UIApplicationMain + 1282 
25 Note        0x000000010e5146c7 main + 135 
26 libdyld.dylib      0x0000000111e99145 start + 1 
27 ???         0x0000000000000001 0x0 + 1 
) 
libc++abi.dylib: terminating with uncaught exception of type NSException 

Answer 1

的问题似乎是在你的谓词定义。请尝试：

fetchRequest.predicate = NSPredicate(format: "name = 'Test2'") 

或

fetchRequest.predicate = NSPredicate(format: "%K = %@", "name", "Test2") 

如果你想添加一个变量。

fetchRequest.predicate = NSPredicate(format: "%K = %@", "name", variable) 

Answer 2

你可以使用context.deleteObject(results?.first as! NSManagedObject)它将编译，但如果它不是一个NSManagedObject它会崩溃。

这显然不是正确的做法。记住：!是代码气味，因为在大多数情况下你不需要它们。

firstObject是NSArray的方法，使用它应该指定results是NSArray类型（即let results: NSArray）的。 Swift标准库相当于first，并返回一个可选值，而deleteObject不接受可选项。所以你应该打开它，你可以同时检查它是否是NSManagedObject。

什么是这样的：

if let results = context.executeFetchRequest(fetchRequest, error:&error), 
     let managedObject = results.first as? NSManagedObject { 
     context.deleteObject(managedObject) 
    }