理解Linq查询

using System;
using System.Linq;
static class Program
{
    static double Square(double n)
    {
        Console.WriteLine("Computing Square(" + n + ")...");
        return Math.Pow(n, 2);
    }

    public static void Main()
    {
        int[] numbers = { 1, 2, 3 };
        var query =
          from n in numbers
          select Square(n); // query只是一个语句，下面的foreach才执行内容
        foreach (var n in query)
            Console.WriteLine(n); // 逐个执行Square(n);方法

        for (int i = 0; i < numbers.Length; i++)
            numbers[i] = numbers[i] + 10;
        Console.WriteLine("- Collection updated -");
        foreach (var n in query)
            Console.WriteLine(n);

        Console.ReadKey();
    }
}

执行结果

Computing Square(1)...
1
Computing Square(2)...
4
Computing Square(3)...
9
- Collection updated -
Computing Square(11)...
121
Computing Square(12)...
144
Computing Square(13)...
169

同样的query,下面的却变了。query只是一个静态的存储语句。
当foreach的时候，才逐个执行查询结果。

再看小例子

using System;
using System.Diagnostics;
using System.Linq;
static class Program
{
    public static void Main()
    {
        var processes =
          Process.GetProcesses()
            .Where(process => process.WorkingSet64 > 20 * 1024 * 1024)
            .OrderByDescending(process => process.WorkingSet64)
            .Select(process => new {
                process.Id,
                Name = process.ProcessName
            });

        foreach (var item in processes)
            Console.WriteLine(item.Name);

        Console.ReadKey();
    }
}

通过图解，能够更加清晰它的流程。

本文转自TBHacker博客园博客，原文链接：http://www.cnblogs.com/jiqing9006/p/7019392.html，如需转载请自行联系原作者