如何在核心数据中使用 NSPredicate 从属性之一获取值

Posted 2023-03-13

【中文标题】如何在核心数据中使用 NSPredicate 从属性之一获取值

【英文标题】：How to get values from one of the Attributes using NSPredicate in Core Data

【发布时间】：2013-03-30 15:23:58

【问题描述】：

我有一个基于核心数据的项目。其中一个属性称为“日期”，我想从该属性中获取值，值以字符串“2013-03”开头，但我只能得到最新值，如字符串“2013-03-30”，如何将所有以“2013-03”开头的值放入NSArray？

NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
NSEntityDescription *entity = [NSEntityDescription entityForName:@"Database" inManagedObjectContext:self.managedObjectContext];
[fetchRequest setEntity:entity];

NSPredicate *predicate = [NSPredicate predicateWithFormat:@"date beginsWith %@",value];
[fetchRequest setPredicate:predicate];
NSSortDescriptor *sortDescription = [[NSSortDescriptor alloc] initWithKey:@"date" ascending:YES];
[fetchRequest setSortDescriptors:@[sortDescription]];

【参考方案1】：

我自己解决 NSMutableArray *array = [[NSMutableArray alloc] init];

NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
NSEntityDescription *entity = [NSEntityDescription entityForName:@"Database" inManagedObjectContext:self.managedObjectContext];
[fetchRequest setEntity:entity];

NSPredicate *predicate = [NSPredicate predicateWithFormat:@"date beginsWith %@",value];
[fetchRequest setPredicate:predicate];
NSSortDescriptor *sortDescription = [[NSSortDescriptor alloc] initWithKey:@"date" ascending:YES];
[fetchRequest setSortDescriptors:@[sortDescription]];

NSError *fetchError = nil;
NSArray *fetchArray = [self.managedObjectContext executeFetchRequest:fetchRequest error:&fetchError];

if ([fetchArray count] > 0)

    for (Database *fetchResult in fetchArray)
    
        [array addObject:fetchResult.date];
    

return array;