核心数据 NSPredicate 检查 BOOL 值 [英] Core Data NSPredicate checking for BOOL value

问题描述

我目前在从数据库中提取所有数据时遇到问题，即 1 个参数为 TRUE.

I am currently having an issue pulling all data from db whereby i.e 1 parameter is TRUE.

我正在使用 NSPredicate，下面是示例代码

I am using NSPredicate and below is a sample code

NSManagedObjectContext *context = managedObjectContext_;

if (!context) {
    // Handle the error.
    NSLog(@"ERROR CONTEXT IS NIL");
}

NSEntityDescription *entity = [NSEntityDescription entityForName:@"tblcontent" inManagedObjectContext:managedObjectContext_];

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

NSPredicate *predicate = [NSPredicate predicateWithFormat:@"bookmarked == YES"];

[request setPredicate:predicate];

我尝试将 predicatewithformat 设置为几乎所有内容，但它仍然没有拉出具有 YES 值的书签.

I tried setting predicatewithformat to almost everything but it still does not pull out bookmarks which have a YES value.

我什至尝试过 (@"bookmarked == %d",YES) 但不走运.我不想获取整个数组，然后通过执行 if(object.bookmarked == YES) .....blabla.

I even tried (@"bookmarked == %d",YES) but with not luck. I don't want to have to get the whole array and then filter it manually by doing if(object.bookmarked == YES) .....blabla.

我会非常感谢您的帮助.

I will really appreciate some help.

非常感谢.

推荐答案

基于 Apple Document 这里，我们可以使用以下两种方法来比较Boolean:

Based on Apple Document Here, we can use the following two methods to compare Boolean:

NSPredicate *newPredicate = [NSPredicate predicateWithFormat:@"anAttribute == %@",[NSNumber numberWithBool:aBool]];
NSPredicate *testForTrue = [NSPredicate predicateWithFormat:@"anAttribute == YES"];

但是，上面的谓词不能把anAttribute为空的谓词取出来.处理空属性需要根据苹果文档这里:

However, the above predicate cannot get out the ones with empty anAttribute. To deal with an empty attribute, you need the following method according to Apple document here:

predicate = [NSPredicate predicateWithFormat:@"firstName = nil"]; // it's in the document

或

predicate = [NSPredicate predicateWithFormat:@"firstName == nil"]; // == and = are interchangeable here

这篇关于核心数据 NSPredicate 检查 BOOL 值的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！