C# LINQ & XML

LINQ(Language-INtegrated Query) 是一種用做查找、存取數據庫或XML文件的語言模式。

是溝通面嚮對象語言與數據庫的方式。與SQL很類似。

using System;
using System.Collections.Generic;
using System.Linq;           //linq namespace
namespace Programming_CSharp
{
    // Simple customer class
    public class Customer           //定義customer對象，構成要搜索的集合
    {
        public string FirstName { get; set; }
        public string LastName { get; set; }
        public string EmailAddress { get; set; }
        // Overrides the Object.ToString() to provide a
        // string representation of the object properties.
        public override string ToString()
        {
            return string.Format("{0} {1}\nEmail:  {2}",
                        FirstName, LastName, EmailAddress);
        }
    }

// Create a customer list with sample data
private  static  List<Customer> CreateCustomerList()
{
   List<Customer> customers = new List<Customer>
   {
      new Customer { FirstName = "Orlando「,LastName = "Gee",
                                    EmailAddress = "orlando0@adventure-works.com"},
      new Customer { FirstName = "Keith「, LastName = "Harris",
                                    EmailAddress = "keith0@adventure-works.com" },
      new Customer { FirstName = "Donna「, LastName = "Carreras",
                                    EmailAddress = "donna0@adventure-works.com" },
      new Customer { FirstName = "Janet「, LastName = "Gates",
                                    EmailAddress = "janet1@adventure-works.com" },
      new Customer { FirstName = "Lucy「, LastName = "Harrington",
                                    EmailAddress = "lucy0@adventure-works.com" }
    };
    return customers;
  }

// 內存中構成Customer的集合

 

   static void Main()    // Main program
   {
       List<Customer> customers = CreateCustomerList();
       // Find customer by first name 
      IEnumerable<Customer> result =  from   customer in customers
      where  customer.FirstName == "Donna"  
      select customer;    //select 放在最後
      Console.WriteLine("FirstName == \"Donna\"");
      foreach (Customer customer in result)
         {    Console.WriteLine(customer.ToString());}  //顯示結果
      customers[3].FirstName = "Donna";                 //修改數據
      Console.WriteLine("FirstName == \"Donna\" (take two)"); //顯示結果
      foreach (Customer customer in result)
         {  Console.WriteLine(customer.ToString());}
    }
  }
}//namespace

Join 關鍵字

內連關鍵字  將兩個數據錶鏈接鏈接

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

 

LINQ中含有關鍵字

where  from  select等

與SQL相似的   where表示篩選條件

from 表示指定的範圍

select 表示查找映射

 

Var關鍵字

var通用數據類型  必須初始化

var num = 1234;
var strnum = "1234";
var classsimple = new class1;