按名称分组的核心数据获取属性

Posted 2023-03-12

【中文标题】按名称分组的核心数据获取属性

【英文标题】：Core Data Fetching Properties with Group By name

【发布时间】：2014-03-19 07:02:55

【问题描述】：

这是我想为Core Data 编写的查询的 SQL 版本：

SELECT ROUNDNAME 
FROM MODELSCHEDULEFIXTURE 
GROUP BY ROUNDNAME 
ORDER BY MATCHID

我使用了下面的代码，但是应用程序崩溃了。

-(NSArray *)getRound


    NSManagedObjectContext * context = ((AFLAppDelegate *)[[UIApplication sharedApplication] delegate] ).managedObjectContext;

    NSFetchRequest *fetch = [NSFetchRequest new];

    NSEntityDescription *entity = [NSEntityDescription entityForName:@"modelschedulefixture" inManagedObjectContext:context];

        NSAttributeDescription* statusDesc = [entity.attributesByName objectForKey:@"roundName"];

    [fetch setPropertiesToFetch:[NSArray arrayWithObjects:statusDesc, nil]];

    [fetch setPropertiesToGroupBy:[NSArray arrayWithObject:statusDesc]];

        [fetch setResultType:NSDictionaryResultType];

    NSError *error = nil;

    NSArray *array= [context executeFetchRequest:fetch error:&error];

    return array;

【问题讨论】：

可能重复 ***.com/questions/4865686/… 看看那里发布的链接。

【参考方案1】：

试试看。

 -(NSArray *)getRound
        NSArray *array=nil;
            NSManagedObjectContext * context = ((AFLAppDelegate *)[[UIApplication sharedApplication] delegate] ).managedObjectContext;
            NSFetchRequest* fetch = [NSFetchRequest fetchRequestWithEntityName:@"modelschedulefixture"];
            NSEntityDescription *entity = [NSEntityDescription entityForName:@"modelschedulefixture" inManagedObjectContext:context];
            NSSortDescriptor *sortDescreptorRound =[[NSSortDescriptor alloc]initWithKey:@"matchid" ascending:YES];
            [fetch setSortDescriptors:[NSArray arrayWithObject:sortDescreptorRound]];
            NSAttributeDescription* statusDesc = [entity.attributesByName objectForKey:@"roundname"];
            [fetch setPropertiesToFetch:[NSArray arrayWithObjects:statusDesc, nil]];
            [fetch setPropertiesToGroupBy:[NSArray arrayWithObject:statusDesc]];
            [fetch setResultType:NSDictionaryResultType];
            NSError *error = nil;
            array = [context executeFetchRequest:fetch error:&error];
        return array;