按核心数据分组会出错

Question

我正在尝试获取请求，我想通过“高级帐户”分组并获取卡号，持卡人姓名和类似的内容。我收到一个奇怪的错误 -

* 由于未捕获的异常'NSInvalidArgumentException'而终止应用程序，原因：'具有GROUP BY组件的查询中的SELECT子句只能包含GROUP BY中命名的属性或聚合函数（（），名称为gCardHolderName ，isOptional 1，isTransient 0，entity Merchant，renamingIdentifier gCardHolderName，验证谓词（ ），警告（ ），versionHashModifier（null）  用户信息 { }，attributeType 700，attributeValueClassName NSString，defaultValue（null）不在GROUP BY中''

我认为这是SQL查询 - SELECT CARDHOLDERNAME，PREMIUM帐户名称来自“MERCHANT”GROUP PREMIUM帐户名称。

高级帐户名称可以相同（对于帐户1，我可以使用不同的持卡人姓名）。

我对这个错误一无所知。这是'我的代码，如果有人可以帮助我 -

pragma mark - FetchRequest方法

- (void)fetchRequest
{
   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];

   [request setFetchBatchSize:15];

   NSSortDescriptor *sortDescriptor1 = [[NSSortDescriptor alloc] initWithKey:@"premiumActName" ascending:NO];

   NSArray *descriptors = [NSArray arrayWithObjects:sortDescriptor1, nil];

   [request setSortDescriptors:descriptors];

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


   NSExpression *keyPathExpression = [NSExpression expressionForKeyPath: @"premiumActName"];
   NSExpression *countExpression = [NSExpression expressionForFunction: @"count:"
                                                          arguments: [NSArray arrayWithObject:keyPathExpression]];
    NSExpressionDescription *expressionDescription = [[NSExpressionDescription alloc] init];
    [expressionDescription setName: @"count"];
    [expressionDescription setExpression: countExpression];
    [expressionDescription setExpressionResultType: NSInteger32AttributeType];

    NSArray *propertiesToFetch= @[accountDesc,cardHolderDesc, expressionDescription];

    [request setPropertiesToFetch:propertiesToFetch];
    [request setPropertiesToGroupBy:[NSArray arrayWithObject:@"premiumActName"]];
    [request setResultType:NSDictionaryResultType];
    [request setReturnsDistinctResults:YES];

    [context save:&anyError];

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

   [distinctResults enumerateObjectsUsingBlock:^(NSDictionary *dict, NSUInteger idx, BOOL *stop) {

      NSLog(@" objects=%@", [dict objectForKey:@"gCardHolderName"]);

   }];

   if(_fetchedResultsController)
   {
      _fetchedResultsController = nil;
   }

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

   if(![_fetchedResultsController performFetch:&anyError])
  {
      NSLog(@"error fetching:%@", anyError);
  }
  [self.membersTblView reloadData];
}

Answer 1

[request setPropertiesToGroupBy：propertiesToFetch]