如何選擇核心數據中的特定數據？

Question

我有一個示例程序，它使用Core Data並在其中加載一個sqlite數據庫。我顯示所有使用此代碼的值

NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init]; 
NSEntityDescription *entity = [NSEntityDescription entityForName:@"Name" 
              inManagedObjectContext:context]; 
[fetchRequest setEntity:entity]; 
NSArray *fetchedObjects = [context executeFetchRequest:fetchRequest error:&error]; 

for (Name *name in fetchedObjects) { 
    NSLog(@"ID: %@", name.nameId); 
    NSLog(@"First Name: %@", name.first); 
    NSLog(@"Middle Name: %@", name.middle); 
    NSLog(@"Last Name: %@", name.last); 
} 

此代碼工作正常，我的問題在於我無法選擇特定的數據/記錄。示例我想選擇ID = 1的記錄。

謝謝！

Answer 1

您必須在執行請求之前使用謂詞（使用NSPredicate）。

類似的東西：

NSPredicate *predicateID = [NSPredicate predicateWithFormat:@"nameID == %d",-1]; 
[fetchRequest setPredicate:predicateID]; 

Answer 2

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

//Add following method to your code. this will help you to get desired result. 
[fetchRequest setPredicate:[NSPredicate predicateWithFormat:@"yourColumnID == %@", yourID]]; 

NSArray *fetchedObjects = [context executeFetchRequest:fetchRequest error:&error]; 

for (Name *name in fetchedObjects) { 
    NSLog(@"ID: %@", name.nameId); 
    NSLog(@"First Name: %@", name.first); 
    NSLog(@"Middle Name: %@", name.middle); 
    NSLog(@"Last Name: %@", name.last); 
}