Question

我正在为我的iOS应用程序使用Core Data，在我的获取请求中，我通过某些属性进行获取GROUP。因为我必须使用GROUP BY，结果类型是NSDictionary而不是托管对象。

表视图工作正常，我面临的唯一问题是删除行。它不会删除该行，并且上下文也不会删除该对象。

我做了一些挖掘，发现如果我的结果类型是一个托管对象，那么上下文可以删除该对象，并且表视图行被删除但然后GROUP BY功能丢失，因为它仅在结果类型为一个NSDictionary对象。

任何帮助都将不胜感激。

这是FETCH REQUEST方法（已编辑）

NSError * anyError = nil;

AppDelegate * applicationDelegate = (AppDelegate *) [[UIApplication sharedApplication] delegate];
NSManagedObjectContext * context = [applicationDelegate managedObjectContext];

NSFetchRequest *request = [[NSFetchRequest alloc] init];
// Edit the entity name as appropriate.
NSEntityDescription *entity = [NSEntityDescription entityForName:@"Merchant" inManagedObjectContext:context];
[request setEntity:entity];

NSSortDescriptor *sortDescriptor = [[NSSortDescriptor alloc] initWithKey:@"premiumActName" ascending:YES];

NSArray *descriptors = [NSArray arrayWithObjects:sortDescriptor, nil];

[request setSortDescriptors:descriptors];

NSPropertyDescription *accountDesc = [[entity propertiesByName] objectForKey:@"premiumActName"];

NSExpressionDescription* objectIdDesc = [NSExpressionDescription new];
objectIdDesc.name = @"objectID";
objectIdDesc.expression = [NSExpression expressionForEvaluatedObject];
objectIdDesc.expressionResultType = NSObjectIDAttributeType;

NSArray *propertiesToFetch= @[accountDesc, objectIdDesc];

[request setPropertiesToFetch:propertiesToFetch];
[request setPropertiesToGroupBy:[NSArray arrayWithObjects:accountDesc, nil]];
[request setResultType:NSDictionaryResultType];
[request setReturnsDistinctResults:YES];

NSArray *distinctResults = [context executeFetchRequest:request error:&anyError];

NSLog(@"function=%s", __PRETTY_FUNCTION__);

NSLog(@" result =%@", distinctResults);

if(!_fetchedResultsController)
{
    _fetchedResultsController = nil;
}

_fetchedResultsController = [[NSFetchedResultsController alloc] initWithFetchRequest:request managedObjectContext:context sectionNameKeyPath:nil cacheName:nil];

if(![_fetchedResultsController performFetch:&anyError])
{
    NSLog(@" Error =%@", anyError);
}

if (![context save:&anyError])
{
    // Handle the error.
}

这是表格视图删除行方法（EDITED）

- (void)tableView:(UITableView *)tableView commitEditingStyle:(UITableViewCellEditingStyle)editingStyle forRowAtIndexPath:(NSIndexPath *)indexPath
{
    AppDelegate *applicationDelegate = (AppDelegate *) [[UIApplication sharedApplication] delegate];
NSManagedObjectContext * context = [applicationDelegate managedObjectContext];

NSDictionary * dictionary = [self.fetchedResultsController objectAtIndexPath:indexPath];
NSManagedObjectID * iod = [dictionary objectForKey:@"objectID"];

NSManagedObject * object = [context objectWithID:iod];

if (editingStyle == UITableViewCellEditingStyleDelete)
{             
    [context deleteObject:object];

    // Commit the change.
    NSError *error = nil;

    if (![context save:&error])
    {
        NSLog(@"Couldn't save: %@", error);
    }
}

    [self.membersTblView reloadData];
}

这也不会删除对象和表视图行！

Answer 1

在你的情况下

NSManagedObject * object = [self.fetchedResultsController objectAtIndexPath:indexPath];

并不真正返回托管对象而是字典，因此[context deleteObject:object]不起作用。

以下可行：

将"objectID"添加到propertiesToFetch。

删除对象：

NSDictionary *dict = [self.fetchedResultsController objectAtIndexPath:indexPath];
NSManagedObjectID *oid = [dict objectForKey:@"objectId"];
NSManagedObject *object = [context objectWithID:oid];
[context deleteObject:object];
[context save:&error];

由于带有字典结果类型的提取结果控制器不会自动更新，您还必须调用：

[self.fetchedResultsController performFetch:&error];
[self.membersTblView reloadData];

试。

NSManaged Object Context无法删除对象

1 个答案: