最近开始学习linq.自己也总结一下,方便以后查阅。
Select 同 Sql 中的 select 类似,即输出我们要的东东,感觉在 linq 中更加强大。
Linq 可以对集合如数组、泛型等操作,这里我们对泛型类型进行举例。建一个类如下:
public class Customer { public Customer(string firstName, string lastName, string city) { FirstName = firstName; LastName = lastName; City = city; } public Customer() {} public string FirstName { get; set; } public string LastName { get; set; } public string City { get; set; } }
1、 select 出对象,cust 是一个Customer 对象。
static void Main(string[] args) { List<Customer> customers = new List<Customer>() { new Customer("Jack", "Chen", "London"), new Customer("Sunny","Peng", "Shenzhen"), new Customer("Tom","Cat","London") }; //使用IEnumerable<T>作为变量 var result =from cust in customers where cust.City == "London" select cust; foreach (var item in result) { Console.WriteLine(item.FirstName+":"+item.City); } Console.Read(); }
2、 select 出对象的属性字段
var result =from cust in customerswhere cust.City == "London" select cust.City
多个属性要用new {}如下:
var result =from cust in customers where cust.City == "London" select new{cust.City,cust.FirstName};
3、 重命名, city 和 name 是随便起的
var result =from cust in customers where cust.City == "London" select new{ city=cust.City, name ="姓名"+ cust.FirstName+""+cust.LastName }; foreach (var item in result) { Console.WriteLine(item.name+":"+item.city); }
4、 直接实例化对象
var result =from cust in customers where cust.City == "London" select new Customer{ City = cust.City, FirstName = cust.FirstName };
5、 selec 中嵌套select
var result =from cust in customers where cust.City == "London" select new{ city = cust.City, name=from cust1 in customers where cust1.City == "London" select cust1.LastName };
时间: 2024-10-10 08:31:20