核心数据排序撷取的请求 [英] Core Data Sort Fetched Request

问题描述

我需要通过ID获取我的数据库和秩序了。因此，例如，我在数据库中，database_id的和内容的两列。当我的NSLog最后一行我得到内容列中的所有行。但是，我需要根据这些database_id的内容行进行排序是1,2,3,4,5,6（升序）。帮助???

  NSFetchRequest *请求= [[NSFetchRequest的alloc]初始化];    NSEntityDescription *耳鼻喉科= [NSEntityDescription entityForName：@的databaseNameinManagedObjectContext：self.managedObjectContext];
    [要求setEntity：ENT];    NSSortDescriptor * SRT = [NSSortDescriptor sortDescriptorWithKey：@database_id的升序：YES];    [要求setSortDescriptors：[NSArray的arrayWithObject：SRT]];    NSError *错误;
    NSArray的*结果= [self.managedObjectContext executeFetchRequest：请求错误：放大器;错误]    如果（！结果）
    {
        //错误
    }
    NSMutableArray里* myArray的= [[NSMutableArray里的alloc] initWithArray：[结果valueForKey：@内容]];
 

解决方案

您 database_id的存储为一个字符串，因此IDS进行排序为字符串：

  1，11，15，2，3，5
 

最好的解决办法是将存放 database_id的作为一个号码（例如，整型32）
数据库。

作为一种解决方法，你可以保持你的字符串，并使用特殊的比较功能
排序描述：

  NSSortDescriptor * SRT = [NSSortDescriptor sortDescriptorWithKey：@database_id的
                 上行：YES
                  选择：@选择（localizedStandardCompare :)]。
 

localizedStandardCompare 做了查找类似比较。特别是，含有串
号根据其数值排序

I need to fetch my database and order it by id. So for example, i have 2 columns in database, database_id and content. When I NSLOG last line i get all rows of "content" column. But I need to sort those "content" rows based on database_id which is 1,2,3,4,5,6 (ascending). Help ???

 NSFetchRequest *request = [[NSFetchRequest alloc] init];

    NSEntityDescription *ent = [NSEntityDescription entityForName:@"databaseName" inManagedObjectContext:self.managedObjectContext];
    [request setEntity:ent];

    NSSortDescriptor *srt = [NSSortDescriptor sortDescriptorWithKey:@"database_id" ascending:YES];

    [request setSortDescriptors:[NSArray arrayWithObject:srt]];

    NSError *error;
    NSArray *result = [self.managedObjectContext executeFetchRequest:request error:&error];

    if (!result)
    {
        //error
    }
    NSMutableArray *myArray = [[NSMutableArray alloc] initWithArray:[result valueForKey:@"content"]];

解决方案

Your database_id is stored as a string and therefore the ids are sorted as strings:

1, 11, 15, 2, 3, 5

The best solution would be to store the database_id as a number (e.g. "Integer 32") in the database.

As a workaround, you can keep your strings, and use a special compare function in the sort descriptor:

NSSortDescriptor *srt = [NSSortDescriptor sortDescriptorWithKey:@"database_id"
                 ascending:YES
                  selector:@selector(localizedStandardCompare:)];

localizedStandardCompare does a "Finder-like" comparison. In particular, strings containing numbers are sorted according to their numerical value.

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