fetchedResultsController的NSPredicate問題

請幫忙！我一直試圖弄清楚這一點太長了。fetchedResultsController的NSPredicate問題

我似乎無法在我的fetchedResultsController方法使用一個NSPredicate：

- (NSFetchedResultsController *)fetchedResultsController {  
if (fetchedResultsController != nil) return fetchedResultsController; 

NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init]; 
NSEntityDescription *entity = [NSEntityDescription entityForName:@"Tweet" inManagedObjectContext:managedObjectContext]; 
[fetchRequest setEntity:entity]; 

NSPredicate *predicate = [NSPredicate predicateWithFormat: @"column == 0"]; 
[fetchRequest setPredicate:predicate]; 

[fetchRequest setReturnsObjectsAsFaults:NO]; 
[fetchRequest setFetchBatchSize:20]; 

NSSortDescriptor *sortDescriptor = [[NSSortDescriptor alloc] initWithKey:@"created_at" ascending:NO]; 
NSArray *sortDescriptors = [[NSArray alloc] initWithObjects:sortDescriptor, nil]; 
[fetchRequest setSortDescriptors:sortDescriptors]; 

NSFetchedResultsController *aFetchedResultsController = [[NSFetchedResultsController alloc] initWithFetchRequest:fetchRequest managedObjectContext:managedObjectContext sectionNameKeyPath:nil cacheName:@"Root"]; 
aFetchedResultsController.delegate = self; 
self.fetchedResultsController = aFetchedResultsController; 

[aFetchedResultsController release]; 
[fetchRequest release]; 
[sortDescriptor release]; 
[sortDescriptors release]; 

return fetchedResultsController; }

然而，在另一種方法，在這裏我簡單的檢查，看看如果一個對象存在，謂語就像一個魅力：

- (BOOL)findObjectWithKey:(NSString *)key andValue:(NSString *)value sortBy:(NSString *)sort { 
NSFetchRequest *request = [[NSFetchRequest alloc] init]; 
NSEntityDescription *entity = [NSEntityDescription entityForName:@"Tweet" inManagedObjectContext:managedObjectContext]; 
[request setEntity:entity]; 

NSPredicate *predicate = [NSPredicate predicateWithFormat: @"%K == %@", key, value]; 
[request setPredicate:predicate]; 

[request setReturnsObjectsAsFaults:NO]; 

NSSortDescriptor *sortDescriptor = [[NSSortDescriptor alloc] initWithKey:sort ascending:YES]; 
NSArray *sortDescriptors = [[NSArray alloc] initWithObjects:sortDescriptor, nil]; 
[request setSortDescriptors:sortDescriptors]; 

NSFetchedResultsController *aFetchedResultsController = [[NSFetchedResultsController alloc] initWithFetchRequest:request managedObjectContext:managedObjectContext sectionNameKeyPath:nil cacheName:@"Root"]; 
aFetchedResultsController.delegate = self; 

NSError *error = nil; 
NSArray *result = [managedObjectContext executeFetchRequest:request error:&error]; 

[aFetchedResultsController release]; 
[request release]; 
[sortDescriptor release]; 
[sortDescriptors release]; 

if ((result != nil) && ([result count]) && (error == nil)) { 
    return TRUE; 
} else { 
    return FALSE; 
}}

我在做什麼錯？提前致謝！

來源

2010-03-16 RyJ

什麼是列？ – 2010-03-16 21:43:16

「列」是核心數據屬性的關鍵。 – RyJ 2010-03-16 21:45:38

假設你的「列」屬性是一個數字，你應該把它比作一個NSNumber對象是這樣的：

NSPredicate *predicate = [NSPredicate predicateWithFormat:@"column == %@",[NSNumber numberWithInteger:0]];

來源

2010-03-16 21:46:51 gerry3

我試過了。沒有工作。 – RyJ 2010-03-16 21:51:28

這並不是說這個特殊的謂詞不起作用（列謂詞）......我似乎無法得到任何謂詞。 – RyJ 2010-03-16 21:54:55

如果我按照我的performFetch這個： NSLog（@「filteredArrayUsingPredicate =％@」，[fetchedResultsController.fetchedObjects filteredArrayUsingPredicate：[NSPredicate predicateWithFormat：@「column ==％@」，[NSNumber numberWithInteger：0]]]）; 返回正確的對象，但這並沒有多大幫助，因爲錯誤的對象（列！= 0）仍然在fetchedResultsController中。 – RyJ 2010-03-16 21:59:41

由於列是實體的屬性，然後你的謂詞邏輯是罰款。你看到哪些結果表明謂詞不起作用？

來源

2010-03-16 23:53:56

fetchedResultsController的NSPredicate問題

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