关于LINQ的一个问题！疑点看红色字体这行！
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
namespace Linq1
{
public class linq2
{
public string firstname { get; set; }
public string lastname { get; set; }
public string emailaddress { get; set; }
public override string ToString()
{
return string.Format("{0} {1}\nemail: {2}", firstname, lastname, emailaddress);
}
}
class Program
{
static void Main(string[] args)
{
List<linq2> customers=createcustomerlist();
IEnumerable<linq2> result = from customer in customers where customer.firstname == "donna" select customer;
Console.WriteLine("firstname=="donna"");
foreach(linq2 customer in result)
{
Console.WriteLine(customer.ToString());
}
customers[3].firstname = "donna";//为什么这里赋值后，result这个变量也改了呢！是不是又自动执行了上面Ienumerable<linq2>这行； Console.WriteLine("firstname="donna"(take two)");
foreach (linq2 customer in result)
{
Console.WriteLine(customer.ToString());
}
}
private static List<linq2> createcustomerlist()
{
List<linq2> customer5=new List<linq2>
{
new linq2{firstname="orlando",lastname="gee",emailaddress="orlando@adventure.com"},
new linq2{firstname="donna",lastname="carreras",emailaddress="donna@adventure.com"}
,new linq2{firstname="bb166",lastname="qiu",emailaddress="donna@adventure.com"}
,new linq2{firstname="jbqiu",lastname="qiujianbin",emailaddress="qq@adventure.com"}
,new linq2{firstname="jbqiu168",lastname="qiujianbin168",emailaddress="qq168@adventure.com"}
};
return customer5;
}
}
}
[解决办法]
List<int> numbers = new List<int>() { 1, 2 };
IEnumerable<int> query = numbers.Select(i => i * 10).ToArray();
numbers.Add(3);
foreach (var item in query)
{
Console.WriteLine(item);//输出：10，20
}
numbers.Clear();//清空numbers集合
foreach (var item in query)
{
Console.WriteLine(item);//输出：10，20
}
要避免linq查询表达式的这个特性可以在查询语句后调用一下方法语法的查询
查询表达式都有重复执行、延迟执行的特性，而方法语法就会立即执行。
[解决办法]
延迟执行（使用的时候才会执行）
这是我看Linq资料里提及相当频繁的一点.
[解决办法]
你将这句:
IEnumerable<linq2> result = from customer in customers where customer.firstname == "donna" select customer;
修改成这样，就不会跟着变了：
List<linq2> result = (from customer in customers where customer.firstname == "donna" select customer).ToList();
这不就是LINQ的延迟查询特性么...
