Performance LINQ与Group、Join和Where Easy在SQL中不是在LINQ中？

我很难理解如何将SQL翻译成LINQ。我想做以下工作，但不知道如何让团队工作

var query = from s in Supplier
            join o in Offers on s.Supp_ID equals o.Supp_ID
            join p in Product on o.Prod_ID equals p.Prod_ID
            where s.City == "Chicago"
            group s by s.City into Results
            select new { Name = Results.Name };

---

我只需要做一些简单的事情，比如显示这个简单查询的产品名称，group by如何处理连接和where？

您没有提供类，所以我假设它们如下所示：

    public class Supplier
    {
        public int SupplierID { get; set; }

        public string SuppierName { get; set; }

        public string City { get; set; }
    }


    public class Product
    {
        public int ProductID { get; set; }

        public string ProductName { get; set; }
    }

    public class Offer
    {
        public int SupplierID { get; set; }

        public int ProductID { get; set; }
    }

然后我添加了用于测试的数据：

它必须给出以下结果：

FirstCompany

SecondCompany您可以尝试以下方法：

   var query = from s in Supplier
                    join o in Offers on s.Supp_ID equals o.Supp_ID
                    join p in Product on o.Prod_ID equals p.Prod_ID
                    where s.City == "Chicago"
                    group s 
                    by new {s.City, s.Name} //added this
                    into Results
                    select new { Name = Results.Key.Name };

您可以按

s.City

对

s

（供应商）进行分组。其结果是

i分组

。也就是说，在分组后，只有

城市

和

供应商

可以到达：对于每个城市，您可以得到其供应商的

IEnumerable

（顺便说一句，这将乘以联接）

因为你也有一个条件，s.City==“Chicago”按城市分组是没有用的。只有一个城市。所以我想你不妨这样做：

from s in Supplier
join o in Offers on s.Supp_ID equals o.Supp_ID
join p in Product on o.Prod_ID equals p.Prod_ID
where s.City == "Chicago"
select new { 
                City = s.City.Name, 
                Supplier = s.Name,
                Product = p.Name,
                ...
            };

---

相当彻底。为什么不将结果数据添加到您的答案中？您是否可以使用导航属性，如

Supplier.Offers

和

Offer.Products

？

    foreach (string supplierName in result)
    {
        Console.WriteLine(supplierName);
    }

   var query = from s in Supplier
                    join o in Offers on s.Supp_ID equals o.Supp_ID
                    join p in Product on o.Prod_ID equals p.Prod_ID
                    where s.City == "Chicago"
                    group s 
                    by new {s.City, s.Name} //added this
                    into Results
                    select new { Name = Results.Key.Name };

from s in Supplier
join o in Offers on s.Supp_ID equals o.Supp_ID
join p in Product on o.Prod_ID equals p.Prod_ID
where s.City == "Chicago"
select new { 
                City = s.City.Name, 
                Supplier = s.Name,
                Product = p.Name,
                ...
            };