NSPredicate:按 NSDate 属性的日期过滤对象 [英] NSPredicate: filtering objects by day of NSDate property

问题描述

我有一个带有 NSDate 属性的核心数据模型.我想按天过滤数据库.我认为该解决方案将涉及 NSPredicate，但我不确定如何将它们组合在一起.

I have a Core Data model with an NSDate property. I want to filter the database by day. I assume the solution will involve an NSPredicate, but I'm not sure how to put it all together.

我知道如何使用 NSDateComponents 和 NSCalendar 比较两个 NSDate 的日期，但是如何使用 过滤它>NSPredicate?

I know how to compare the day of two NSDates using NSDateComponents and NSCalendar, but how do I filter it with an NSPredicate?

也许我需要在我的 NSManagedObject 子类上创建一个类别，它可以返回一个只有年、月和日的空日期.然后我可以在 NSPredicate 中进行比较.这是您的建议，还是有更简单的方法?

Perhaps I need to create a category on my NSManagedObject subclass that can return a bare date with just the year, month and day. Then I could compare that in an NSPredicate. Is this your recommendation, or is there something simpler?

推荐答案

给定一个 NSDate * startDate 和 endDate 和一个 NSManagedObjectContext * moc:

Given a NSDate * startDate and endDate and a NSManagedObjectContext * moc:

NSPredicate *predicate = [NSPredicate predicateWithFormat:@"(date >= %@) AND (date <= %@)", startDate, endDate];
NSFetchRequest *request = [[[NSFetchRequest alloc] init] autorelease];
[request setEntity:[NSEntityDescription entityForName:@"EntityName" inManagedObjectContext:moc]];
[request setPredicate:predicate];

NSError *error = nil;
NSArray *results = [moc executeFetchRequest:request error:&error];

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