为Any（）方法动态构建LINQ过滤器？ [英] Dynamically build LINQ filter for the Any() method?

问题描述

Any（）接收一个Func
如何动态构建过滤器？即：

Any() takes in a Func how can I dynamically build up filters to it? ie:

var filter = () a=> a.Text == "ok";//add the first filter
if (flag)
    filter += () a=> a.ID == 5;//add the second filter << obviously this doesn't work.

list.Any(filter);

我还看到了代码，结合了一个表达式>的列表，但我不是得到这个工作，因为我不知道如何转换为Func

I've also seen code out there to combine a list of Expression> , but i'm not getting that to work because I don't know how to convert it toFunc

任何帮助将不胜感激。

推荐答案

您可以通过从当前的其他过滤器调用过滤器，如下所示：

You can compose filters by calling other filters from your current one, like this:

var input = new[] {"quick", "brown", "fox", "jumps"};
Func<string,bool> filter1 = a => a == "quick";
Func<string,bool> filter2 = a => filter1(a) || a.Length == 3;
foreach (var s in input.Where(filter2)) {
    Console.WriteLine(s);
}

打印

quick
fox

演示在ideone 。

您可以对任何基于谓词的方法使用相同的方法LINQ的功能，包括任何：

You can use the same approach for any predicate-based functions of LINQ, including Any:

if (input.Any(filter2)) {
    ...
}

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