Question

您好，

我正在开发一个iphone应用程序，我必须借助核心数据NSPredicate对象从sqlite表中获取数据。

我想在随机的基础上获取记录，而不进行任何排序。

喜欢：

SELECT * FROM zquestionsdata where zquestiontype='Logic' ORDER BY RANDOM()

如何通过NSPredicate实施？

感谢.......

Answer 1

你需要编写像这样的代码

-(NSMutableArray *)getRandomArrayFromDB
{
    NSMutableArray *fetchResults;
        NSString *entityName=@"questionsdata";
        NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
        NSEntityDescription *entity = [NSEntityDescription entityForName:entityName inManagedObjectContext:globalManagedObjectContext];
        [fetchRequest setEntity:entity];

        fetchResults = [NSMutableArray arrayWithArray:[globalManagedObjectContext executeFetchRequest:fetchRequest error:nil]];
        [fetchRequest release];
    NSString *cat=@"Logic";
            [fetchResults filterUsingPredicate:[NSPredicate predicateWithFormat:@"questiontype == %@",cat]];

// sort it in random order

NSUInteger count = [fetchResults count];
    for (NSUInteger i = 0; i < count; ++i) {
        // Select a random element between i and end of array to swap with.
        int nElements = count - i;
        int n = (random() % nElements) + i;
        [fetchResults exchangeObjectAtIndex:i withObjectAtIndex:n];
    }

return fetchResults;
}

调用此方法，它可以提供您想要的内容。

在iphone NSPredicate中按Random（）子句排序

1 个答案: