我可以使用什么Linq查询来按类别返回所有产品的计数? [英] What Linq query can I use to return a count of all products by Category?

问题描述

给出以下表格结构，如何使用Linq查询返回类别名称列表和该类别中产品的总数?

Given the following table structure, how can I use a Linq query to return a list of Category names and the total count of products in that category?

Category
---------
ID
Name

Product
---------
ID 
IDCategory
Name

我的理想回报是:

Clothes 156
Electronics 2149
Utensils 412

等等.

感谢您的有用建议，我现在有这个建议:

Thanks for the helpful suggestions, I now have this:

class Program
{
    static void Main(string[] args)
    {
        MyDatabaseEntities entities = new MyDatabaseEntities();

        var result = from c in entities.Categories
                        join p in entities.Products on c.ID equals p.IDCategory
                        group p by c.Name into g
                        select new
                        {
                            Name = g.Key,
                            Count = g.Count()
                        };

        Console.WriteLine(result.ToString());
        Console.ReadLine();
    }
}

如何精确输出结果?在调试过程中，我可以查看变量值，并且它具有所需的内容，我只是不知道如何显示它.

How exactly can I output what is in the result? During debugging I can view the variables values and it has what I need I just don't know how to show it.

推荐答案

from c in Category
join p in Product on c.ID equals p.IDCategory
group p by c.Name into g
select new
{
    Name = g.Key,
    Count = g.Count()
}

这将适用于任何LINQ风格，并按名称而不是类别ID进行分组.

That will work in any flavor of LINQ, and groups by the Name, rather than the ID of category.

如果您使用的是LINQ to Entities，这可能会更快，并且使用ID而不是名称进行分组:

If you are using LINQ to Entities, this may be faster, and groups on ID rather than name:

from p in Product
group p by p.Category into g
select new
{
    Name = g.Key.Name,
    Count = g.Count()
}

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