如何正確設置一個NSPredicate一個一對多的關係，要檢查所有腦幹對象

Question

我有兩個表TRIP和ALERT

關係是1對多 之旅可以包含1或大於1級的警報， 我想獲取那些誰包含警報

我做取這樣的要求之旅，PLZ資產我親愛的

- （NSFetchRequest *）fetchRequestGetTriphavingAlert { NSFetchRequest * fetchRequest = [[NSFetchRequest的alloc]初始化]

NSEntityDescription *trip = [NSEntityDescription entityForName:@"Trip" inManagedObjectContext:self.managedObjectContext]; 
[fetchRequest setEntity:trip]; 

NSPredicate *predicate = [NSPredicate predicateWithFormat:@"alert == %@",!NULL]; 
[fetchRequest setPredicate:predicate]; 
NSSortDescriptor *sort = [NSSortDescriptor sortDescriptorWithKey:@"startDate" ascending:YES]; 
[fetchRequest setSortDescriptors:[NSArray arrayWithObject:sort]]; 
return fetchRequest; 

}

Answer 1

試試這個：

NSPrediate *predicate = [NSPredicate predicateWithFormat:@"alert.@count > 0"];