如何：对 Join 子句的结果进行排序（C# 编程指南）

项目
02/21/2013

此示例演示如何对联接运算的结果进行排序。请注意，排序是在联接之后执行的。尽管可以在联接之前将 orderby 子句用于一个或多个源序列，但通常我们不建议这样做。某些 LINQ 提供程序可能不会在联接之后保留排序。

示例

此查询将创建一个分组联接，然后基于类别元素（仍然在范围中）对组进行排序。在匿名类型初始值设定项中，子查询将对产品序列中的所有匹配元素进行排序。

     class HowToOrderJoins
     {
         #region Data
         class Product
         {
             public string Name { get; set; }
             public int CategoryID { get; set; }
         }

         class Category
         {
             public string Name { get; set; }
             public int ID { get; set; }
         }

         // Specify the first data source.
         List<Category> categories = new List<Category>()
 { 
     new Category(){Name="Beverages", ID=001},
     new Category(){ Name="Condiments", ID=002},
     new Category(){ Name="Vegetables", ID=003},
     new Category() {  Name="Grains", ID=004},
     new Category() {  Name="Fruit", ID=005}            
 };

         // Specify the second data source.
         List<Product> products = new List<Product>()
{
   new Product{Name="Cola",  CategoryID=001},
   new Product{Name="Tea",  CategoryID=001},
   new Product{Name="Mustard", CategoryID=002},
   new Product{Name="Pickles", CategoryID=002},
   new Product{Name="Carrots", CategoryID=003},
   new Product{Name="Bok Choy", CategoryID=003},
   new Product{Name="Peaches", CategoryID=005},
   new Product{Name="Melons", CategoryID=005},
 };
         #endregion
         static void Main()
         {
             HowToOrderJoins app = new HowToOrderJoins();
             app.OrderJoin1();

             // Keep console window open in debug mode.
             Console.WriteLine("Press any key to exit.");
             Console.ReadKey();

         }

         void OrderJoin1()
         {
             var groupJoinQuery2 =
                 from category in categories
                 join prod in products on category.ID equals prod.CategoryID into prodGroup
                 orderby category.Name
                 select new
                 {
                     Category = category.Name,
                     Products = from prod2 in prodGroup
                                orderby prod2.Name
                                select prod2
                 };

             foreach (var productGroup in groupJoinQuery2)
             {
                 Console.WriteLine(productGroup.Category);
                 foreach (var prodItem in productGroup.Products)
                 {
                     Console.WriteLine("  {0,-10} {1}", prodItem.Name, prodItem.CategoryID);
                 }
             }
         }
         /* Output:
             Beverages
               Cola       1
               Tea        1
             Condiments
               Mustard    2
               Pickles    2
             Fruit
               Melons     5
               Peaches    5
             Grains
             Vegetables
               Bok Choy   3
               Carrots    3
          */
     }