GroupBy with linq方法语法(不是查询语法)

Question

如果我使用扩展方法语法,以下查询将如何显示？

var query = from c in checks
group c by string.Format("{0} - {1}", c.CustomerId, c.CustomerName) 
into customerGroups
select new { Customer = customerGroups.Key, Payments = customerGroups }

Answer 1

它看起来像这样:

var query = checks
    .GroupBy(c => string.Format("{0} - {1}", c.CustomerId, c.CustomerName))
    .Select (g => new { Customer = g.Key, Payments = g });

Answer 2

一,基本答案:

var query = checks.GroupBy<Customer, string>(delegate (Customer c) {
    return string.Format("{0} - {1}", c.CustomerId, c.CustomerName);
}).Select(delegate (IGrouping<string, Customer> customerGroups) {
    return new { Customer = customerGroups.Key, Payments = customerGroups };
});

那你怎么自己弄清楚这些东西呢？

首先,从这里下载Reflector ,然后安装它.

然后构建一个示例程序,就像一个小型控制台程序,包含您要分析的代码.这是我写的代码:

using System;
using System.Collections.Generic;
using System.Linq;

namespace ConsoleApplication11
{
    public class Customer
    {
        public Int32 CustomerId;
        public Int32 CustomerName;
    }

    class Program
    {
        static void Main(string[] args)
        {
            var checks = new List<Customer>();
            var query = from c in checks
                        group c by String.Format("{0} - {1}", c.CustomerId, c.CustomerName)
                            into customerGroups
                            select new { Customer = customerGroups.Key, Payments = customerGroups };
        }
    }
}

然后你构建它,并打开反射器,并要求它打开有问题的.exe文件.

然后导航到相关方法,在我的例子中ConsoleApplication11.Program.Main.

这里的技巧是转到Reflector的选项页面,并要求它显示C#2.0语法,它将用适当的静态方法调用替换Linq.这样做给了我以下代码:

private static void Main(string[] args)
{
    List<Customer> checks = new List<Customer>();
    var query = checks.GroupBy<Customer, string>(delegate (Customer c) {
        return string.Format("{0} - {1}", c.CustomerId, c.CustomerName);
    }).Select(delegate (IGrouping<string, Customer> customerGroups) {
        return new { Customer = customerGroups.Key, Payments = customerGroups };
    });
}

现在,当然这个代码可以用lambdas和类似的东西写得 更漂亮,就像@mquander所展示的那样,但是使用Reflector,至少你应该能够理解所涉及的方法调用.