使用NSPredicate按日期过滤的coredata不返回任何内容

Question

嗨,我是这个coredata的新手.我有两个实体CategoryList和ExpenseList.CategoryList包含两个属性
1.dates(nsdate)
2.categories(nsstring)
以及与ExpenseList的多个关系,关系名称为"expenseList"ExpenseList由1.amountSpent(float)组成.
我只是想知道了解coredata中的关系特征.当我试图创建一个nspredicate来按特定日期过滤数据时,它什么也没有返回.我只想过滤CategoryList实体中的类别属性内容以获取特定日期.这是我的代码

-(void) callingByDate
{


NSManagedObjectContext *managedObjectContext = [self managedObjectContext];

NSEntityDescription *categoryL = [NSEntityDescription entityForName:@"CategoryList" inManagedObjectContext:managedObjectContext];

NSSortDescriptor *dateSort = [[NSSortDescriptor alloc]initWithKey:@"date" ascending:YES];

NSArray *sortDescriptors = [[NSArray alloc]initWithObjects:dateSort, nil];

NSPredicate *predicate = [NSPredicate predicateWithFormat:@"dates == %@",date];



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



[dateFetch setSortDescriptors:sortDescriptors];

[dateFetch setEntity:categoryL];

[dateFetch setPredicate:predicate];



NSMutableArray *results = [[managedObjectContext executeFetchRequest:dateFetch error:nil] mutableCopy];

if([results count] > 0)

    NSLog(@"results found");

else

    NSLog(@"no results found");

}

当我在nslog区域执行此代码时,它显示"找不到结果".我无法弄清楚为什么.提前致谢

这是我的代码,以找到一天的结束和开始

-(NSDate *)beginningOfDay:(NSDate *)date;

 {

 NSDate *dat = [NSDate date];

 NSCalendar *cal = [NSCalendar currentCalendar];

 NSDateComponents *components = [cal components:( NSMonthCalendarUnit | NSYearCalendarUnit | NSHourCalendarUnit | NSMinuteCalendarUnit | NSSecondCalendarUnit ) fromDate:dat];

[components setHour:0];

[components setMinute:0];

[components setSecond:0];



return [cal dateFromComponents:components];





 }



-(NSDate *)endOfDay:(NSDate *)date;

{

NSDate *dat = [NSDate date];

NSCalendar *cal = [NSCalendar currentCalendar];

NSDateComponents *components = [cal components:( NSMonthCalendarUnit | NSYearCalendarUnit | NSHourCalendarUnit | NSMinuteCalendarUnit | NSSecondCalendarUnit ) fromDate:dat];

[components setHour:23];

[components setMinute:59];

[components setSecond:59];



return [cal dateFromComponents:components];

当我的nslog,结果显示是开始日-2013-04-30 18:30:00 +0000 endOfDay -2013-05-01 18:29:59 +0000

Answer 1

date实际上是一个时间戳,所以==使用它只会返回具有确切时间戳的项目.

要获取特定日期的所有条目,您需要获取NSDate一天的开始(startOfDay)和NSDate一天的结束(endOfDay)然后修改谓词以使用以下内容获取这两个值之间的日期:

NSPredicate *predicate = [NSPredicate predicateWithFormat:@"dates >= %@ AND dates >= %@", startOfDay, endOfDay];

要计算startOfDay,endOfDay您可以手动自己完成,也可以使用其他库来计算它,例如https://github.com/erica/NSDate-Extensions.