LINQ可以很方便的对数据源进行筛选、排序和分组操作。
格式 ：from …… 例： from customer(范围变量) in customers(数据源)
where …… where customer.Firstname=="sadas" (筛选的条件)
select …… select customer (映射，具体要选的主体或属性)
LINQ查询式可以立刻执行
foreach (Customer customer in result) {……；}
customers[3].FirstName = "Donna";
foreach (Customer customer in result){…;} rusult将立刻改变
如果不想改变，可以预存变化前的值，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){…;}
}
连接 join
[data source 1] join [data source 2] on [join condition]
将两个数据源按照一定条件连接在一起
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中数据
var 关键字能够代替局部变量的类型
foreach (var ca in result) //
{
Console.WriteLine(string.Format("{0} Address: {1}",
ca.Customer, ca.Address));
}
分组 group
var result = from address in addresses
group address by address.Name;//按照条件 address.Name 分组
foreach (var gp in result)
{
Console.WriteLine("{0}", gp.Key); //~.key代表分组条件，即address.Name
foreach (var a in gp)
Console.WriteLine(" {0}", a);
}