检查coredata对象是否为nil
问题描述：
我想找出核心数据中的对象，我的代码：
I want to find out the objects in the core data, my code:
类型：
signedDate （日期）
alarmDate （日期）
starTime （NSDate）
endTime （NSDate）
NSString *str = @"(signedDate >= %@) AND (signedDate < %@) AND (alarmDate == nil)";
NSPredicate *predicate = [NSPredicate predicateWithFormat:str, starTime, endTime];
[request setPredicate:predicate];
NSArray *results=[context executeFetchRequest:request error:nil];
谓词错了吗？
如何判断coredata对象为nil？
谓词应该是什么？
predicate is wrong ? How to judge an coredata object is nil? What the predicate should be?
答
我认为谓词语法不需要== nil。
仅使用一个=
I don't think the predicate syntax calls for == nil. Use only one =
NSString *str = @"(signedDate >= %@) AND (signedDate < %@) AND (alarmDate = nil)";
上面的代码可以正常工作。
Your code above works right. It should be YES since it's nil.
BOOL ok;
predicate = [NSPredicate predicateWithFormat:@"firstName = nil"];
ok = [predicate evaluateWithObject:[NSDictionary dictionary]];
ok = [predicate evaluateWithObject:
[NSDictionary dictionaryWithObject:[NSNull null] forKey:@"firstName"]];