在谓词中使用@min

本文介绍了在谓词中使用@min的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！ 问题描述

我当前获取@min或@max值的版本是:

My current version for get @min or @max value is:

for (NSManagedObject *destination in allSpecifics) { [allRates addObject:[destination valueForKey:@"rate"]]; } NSExpression *arrayExpression = [NSExpression expressionForConstantValue: allRates]; NSArray *argumentArray = [NSArray arrayWithObject: arrayExpression]; NSExpression* expression = [NSExpression expressionForFunction:@"min:" arguments:argumentArray]; id result = [expression expressionValueWithObject: nil context: nil]; NSNumber *rateForAdd = result;

allSpecific是NSManagedObjects的数组.看起来这不是一种填充对象数组的好方法(内存和处理时间成本).也许有人可以帮助重构它?

allSpecific is array of NSManagedObjects. Looks like is a not good way to fill array of objects before (memory and process time cost). Probably somebody can help refactor it?

推荐答案

因此，您有一个 NSManagedObjects 的数组( allSpecifics )，并且这些对象都有一个率属性?如果正确，那么:

So you have an array (allSpecifics) of NSManagedObjects, and these objects have a rate property? If that's correct then:

要查找:

• 最低费率值: NSNumber * minimumRate = [allSpecifics valueForKeyPath:@"@ min.rate"];
• 最大速率值: NSNumber * minimumRate = [allSpecifics valueForKeyPath:@"@ max.rate"];
• 平均费率值: NSNumber * minimumRate = [allSpecifics valueForKeyPath:@"@ avg.rate"];
• 总费率值: NSNumber * minimumRate = [allSpecifics valueForKeyPath:@"@ sum.rate"];