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我是第一次在这里提问，对不起，我找不到类似的。所以，我需要更新实体“城市”属性中的数据 - @“名称”。例如，在我的核心数据中，我已经有 @"New York"、@"Boston"。通过解析 XML 我有 NSMutableArray *Cities = (@"New York", @"Boston", @"Los Angeles", @"Washington");

- (void)configureCell:(UITableViewCell *)cell atIndexPath:(NSIndexPath *)indexPath
{
    NSString *attributeString = @"name";
    NSManagedObject *object = [self.fetchedResultsController objectAtIndexPath:indexPath];
//save to the TableView
cell.textLabel.text = [[object valueForKey:attributeString] description];
if ((indexPath.row + 1) == numberOfSectionsInTableView && (self.isParsingDone))
        [self.insertNewObjectToCities:nil];
//When coredata updating - tableView is also updating automatically


//Here is just adding new data, but I do not know how to update
- (void)insertNewObjectToCities_translation:(id)sender
{
     NSManagedObjectContext *context = [self.fetchedResultsController managedObjectContext];
NSEntityDescription *entity = [[self.fetchedResultsController fetchRequest] entity];
NSManagedObject *newManagedObject = [NSEntityDescription insertNewObjectForEntityForName:[entity name] inManagedObjectContext:context];
NSString *attributeString = @"name";

if (![[self.parseCities.Cities objectAtIndex:i] isEqualToString:[newManagedObject valueForKey:attributeString]])
{
    [newManagedObject setValue:[self.parseCities.Cities objectAtIndex:i] forKey:attributeString];
    NSLog(@"OBBB %@", [self.parseCities.Cities objectAtIndex:i]);
    NSLog(@"dessss %@", [[newManagedObject valueForKey:attributeString] description]);

    i++;

    if (i==[self.parseCities.Cities count]) 
    {
        i = 0;
        return;
    }
    else 
    {
        NSLog(@"valueForKey %@", [newManagedObject valueForKey:attributeString]);
        [self insertNewObjectToCities_translation:nil];
    }
}
else 
{
    NSLog(@"else");
    return;
}

// Save the context.
NSError *error = nil;
if (![context save:&error]) {
    // Replace this implementation with code to handle the error appropriately.
    // abort() causes the application to generate a crash log and terminate. You should not use this function in a shipping application, although it may be useful during development. 
    NSLog(@"Unresolved error %@, %@", error, [error userInfo]);
    abort();
}

}
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1 回答 1

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要更新托管对象，首先需要获取它，对 fetched 中的字段进行任何更改NSManagedObject，然后保存用于获取对象的上下文。如果insertNewObjectForEntityForName再次调用，它每次都会插入一个新的托管对象，即使它已经存在于 Core Data 中。

It's quite slow to fetch a single object every time you need to check and see if a new one needs to be added. You might want to cache the objects you currently have loaded (or their unique identifying field) into an NSArray or NSSet so you can check that for membership, instead.

于 2012-05-14T17:17:04.193 回答