如何使用核心數據更新和刪除需要記錄的表格

Question

我正在學習核心數據 如何使用核心數據刪除和更新數據。我曾經在上傳和獲取。我需要編寫刪除和更新的方法。請告訴我如何使用核心數據更新和刪除重新編碼。

下面我編寫了使用核心數據從表中上載和提取數據的代碼。

for (NSManagedObject *managedObject in items) { 
    [self.managedObjectContext deleteObject:managedObject]; 
    DebugLog(@"%@ object deleted",entityDescription); 
} 
if (![self.managedObjectContext save:&error]) { 
    DebugLog(@"Error deleting %@ - error:%@",entityDescription,error); 
} 

更新以類似的方式進行，取對象需要，更改：

-(void)uploadData 
{ 
    Employee *empObj=(Employee *)[NSEntityDescription insertNewObjectForEntityForName:@"Employee" inManagedObjectContext:self.managedObjectContext]; 


    empObj.empId=[NSNumber numberWithInt:12345]; 
    empObj.empSalary=[NSNumber numberWithInt:25000]; 

    empObj.empName=@"Venu"; 
    empObj.empDesignation=@"Programmer"; 
    empObj.empExp=@"2 Years"; 

    if ([self.managedObjectContext hasChanges]) 
    { 
     [self.managedObjectContext save:nil]; 
    } 

} 
-(void)fetchData 
{ 
    NSEntityDescription *empEntity = [NSEntityDescription entityForName:@"Employee" inManagedObjectContext:self.managedObjectContext]; 

    // Setup the fetch request 
    NSFetchRequest *request = [[NSFetchRequest alloc] init]; 
    [request setEntity:entity]; 

    NSArray *fatherArray=[self.managedObjectContext executeFetchRequest:request error:nil]; 

    [request setEntity:empEntity]; 

    NSArray *empArray=[self.managedObjectContext executeFetchRequest:request error:nil]; 

    for (int i=0; i<[empArray count]; i++) 
    { 
     printf("\n=================================Recored== %d==================================== ",i); 

     Employee *empObj=[empArray objectAtIndex:i]; 
     printf("\n obj.empName========= %s",[empObj.empName UTF8String]); 
     printf("\n obj.empDesignation========= %s",[empObj.empDesignation UTF8String]); 
     printf("\n obj.empExp========= %s",[empObj.empExp UTF8String]); 
     printf("\n obj.empId========= %d",[empObj.empId intValue]); 
     printf("\n obj.empSalary========= %d",[empObj.empSalary intValue]); 
     printf("\n============================================================================= "); 

    } 
} 

Answer 1

我正在做一個涉及核心數據的項目，我想 想分享一些關於它的東西。

很明顯，在刪除或更新記錄之前，您需要 來檢索該記錄。

使用與EMPID 12345員工爲例，

一）刪除

NSFetchRequest *request = [[NSFetchRequest alloc] init]; 
NSEntityDescription *entity = [NSEntityDescription entityForName:@:@"Employee"             
              inManagedObjectContext:self.managedObjectContext]; 
[request setEntity:entity]; 


NSPredicate *pred = [NSPredicate predicateWithFormat:[NSString stringWithFormat:@"empId = %d", 12345]]; 
[request setPredicate:pred]; 


NSArray *empArray=[self.managedObjectContext executeFetchRequest:request error:nil]; 
[request release]; 

if ([empArray count] > 0){ 
    Employee *employee = [empArray objectAtIndex:0]; 
    [self.managedObjectContext deleteObject:employee]; 
    [self.managedObjectContext save:nil]; 
} 

二）更新

NSFetchRequest *request = [[NSFetchRequest alloc] init]; 
NSEntityDescription *entity = [NSEntityDescription entityForName:@:@"Employee"  
              inManagedObjectContext:self.managedObjectContext]; 
[request setEntity:entity]; 

NSPredicate *pred = [NSPredicate predicateWithFormat:[NSString stringWithFormat:@"empId = %d", 12345]]; 
[request setPredicate:pred]; 

NSArray *empArray=[self.managedObjectContext executeFetchRequest:request error:nil]; 
[request release]; 

if ([empArray count] > 0){ 
    Employee *employee = [empArray objectAtIndex:0]; 

    employee.empSalary=[NSNumber numberWithInt:45000]; 

    employee.empName=@"John"; 
    employee.empDesignation=@"Analysist"; 
    employee.empExp=@"4 Years"; 

    [self.managedObjectContext save:nil]; 
} 

Answer 2

成功獲取請求後，你可以簡單地詢問被管理的ObjectContext刪除它們刪除對象值，並保存上下文。