C#課後小試6

標籤：

LINQ可以很方便的對資料來源進行篩選、排序和分組操作。

   格式 ：from   ……      例：          from customer(範圍變數) in customers(資料來源)

           where  ……                      where customer.Firstname=="sadas"  (篩選的條件)

            select  ……                     select customer     (映射，具體要選的主體或屬性)

LINQ查詢式可以立刻執行

foreach (Customer customer in result) {……；}

customers[3].FirstName = "Donna";

foreach (Customer customer in result){…;}  rusult將立刻改變

如果不想改變，可以預存變化前的值，可以使用tolist() toarry()

 static void Main()

 {

   List<Customer> customers = CreateCustomerList();

   IEnumerable<Customer> result = from customer in customers

      where customer.FirstName == "Donna“ select customer;

 

    List<Customer> cachedResult = result.ToList<Customer>();   //存值，需要之前的值就去查之前存的地方。

 

    foreach (Customer customer in cachedResult){…;}

    customers[3].FirstName = "Donna";

    Console.WriteLine("FirstName == \"Donna\" (take two)");

    foreach (Customer customer in cachedResult){…;}

}

 

串連 join

 [data source 1] join [data source 2] on [join condition]

將兩個資料來源按照一定條件串連在一起

customer in customers join address in addresses on customer.Name equals address.Name；

排序 orderby

var result =from customer in Customers

                orderby customer.LastName

                 select customer;  //升序排Lastname中資料

var 關鍵字能夠代替局部變數的類型

     foreach (var ca in result) //

     {

         Console.WriteLine(string.Format("{0}\nAddress: {1}",

             ca.Customer, ca.Address));

      }

 

分組 group

var result = from address in addresses

      group address by address.Name;//按照條件 address.Name 分組

foreach (var gp in result)

{

      Console.WriteLine("{0}", gp.Key); //~.key代表分組條件，即address.Name

       foreach (var a in gp)

             Console.WriteLine("\t{0}", a);

 }

 

C#課後小試6