上一篇【Generic List Sorting in C# 3.0】講到只要有繼承 IEnumerable 介面或是 IEnumerable<T> 介面，現在都內建 OrderBy 與 OrderByDescending 的 Extension Methods 新功能。但是如果該欄位的值相等，要繼續比較其他的指定欄位，就需要 ThenBy、ThenByDescending 囉。

(1) 一樣建立 Product 類別作為示範，該類別擁有 int 型態的 ID 屬性、string 型態的 Name 屬性、double 型態的 Pricce 屬性、DateTime 型態的 ShipDate 屬性，覆寫 ToString() 方法方便我們列印。

(2) 利用 Collection Initializers 建立實例

   1:  var pList = new List<Product>
   2:              {
   3:                      new Product {ID = 1, Name = "A", Price = 19, ShipDate = new DateTime(2006, 1, 19)}, 
   4:                      new Product {ID = 7, Name = "C", Price = 17, ShipDate = new DateTime(2006, 10, 17)}, 
   5:                      new Product {ID = 7, Name = "B", Price = 17, ShipDate = new DateTime(2007, 2, 12)}, 
   6:                      new Product {ID = 5, Name = "D", Price = 237, ShipDate = new DateTime(2005, 9, 11)}
   7:              };

(3) 直接進入範例：

   1:  // 依照 ID 欄位升冪排序、在依 Name 欄位升冪排序
   2:  foreach (var product in pList.OrderBy(p => p.ID).ThenBy(p => p.Name))
   3:  {
   4:      Console.WriteLine(product.ToString());
   5:  }
   6:  Console.WriteLine();
   7:   
   8:  // 依照 ID 欄位升冪排序、在依 Price 欄位降冪排序、在依 Price 欄位升冪排序
   9:  foreach (var product in pList.OrderBy(p => p.ID).ThenByDescending(p => p.Price).ThenBy(p => p.ShipDate))
  10:  {
  11:      Console.WriteLine(product.ToString());
  12:  }
  13:  Console.WriteLine();

(4) 輸出結果：

   1:  // 依照 ID 欄位升冪排序、在依 Name 欄位升冪排序
   2:  ID: 1, Name: A, Price: 19, ShipDate: 2006/1/19
   3:  ID: 5, Name: D, Price: 237, ShipDate: 2005/9/11
   4:  ID: 7, Name: B, Price: 17, ShipDate: 2007/2/12
   5:  ID: 7, Name: C, Price: 17, ShipDate: 2006/10/17
   6:   
   7:  // 依照 ID 欄位升冪排序、在依 Price 欄位降冪排序、在依 Price 欄位升冪排序
   8:  ID: 1, Name: A, Price: 19, ShipDate: 2006/1/19
   9:  ID: 5, Name: D, Price: 237, ShipDate: 2005/9/11
  10:  ID: 7, Name: C, Price: 17, ShipDate: 2006/10/17
  11:  ID: 7, Name: B, Price: 17, ShipDate: 2007/2/12