使用 linq 方法语法（不是查询语法）的 GroupBy

发布于 2024-07-23 08:55:30 字数 246 浏览 6 评论 0原文

如果我使用扩展方法语法，以下查询会是什么样子？

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 }

原文

How would the following query look if I was using the extension method syntax?

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 }

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尽揽少女心 2024-07-30 08:55:30

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 });

It would look like this:

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

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蓝海 2024-07-30 08:55:30

首先，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 };
});

那么，你自己如何弄清楚这些事情呢？

首先，从此处下载 Reflector 并安装。

然后构建一个示例程序，例如一个小型控制台程序，其中包含您要分析的代码。这是我编写的代码：

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 };
        }
    }
}

然后构建它，打开 Reflector，并要求它打开有问题的 .exe 文件。

然后导航到有问题的方法，在我的例子中是 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，这将用适当的静态方法调用替换 Linq。这样做会给我以下代码：

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，当然可以使用 lambda 和类似的代码编写更漂亮的代码，就像 @mquander< /a> 显示，但使用 Reflector ，至少您应该能够理解所涉及的方法调用。

First, the basic answer:

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 };
});

Then, how do you figure out these things yourself?

First, download Reflector from here, and install it.

Then build a sample program, like a smallish console program, containing the code you want to analyze. Here's the code I wrote:

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 };
        }
    }
}

Then you build that, and open reflector, and ask it to open the .exe file in question.

Then you navigate to the method in question, which in my case was ConsoleApplication11.Program.Main.

The trick here is to go to the options page of Reflector, and ask it to show C# 2.0 syntax, which will substitute Linq with the appropriate static method calls. Doing that gives me the following code:

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 };
    });
}

Now, of course this code can be written a bit prettier with lambdas and similar, like what @mquander showed, but with Reflector, at least you should be able to understand the method calls being involved.

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