LinQ综合应用实例

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Threading.Tasks;

public partial class test : System.Web.UI.Page
{
protected void Page_Load(object sender, EventArgs e)
{
string[] names = { "Wang", "Biao", "WangBiao", "Kingtiger" };
var q1 = names.Where(a => a.StartsWith("W"));//直接查询
var q2 = from a in names
where a.StartsWith("W")
select a;//linq查询
var q3 = from a in names
where a.StartsWith("W")
orderby a descending
select a;//linq查询，包括排序,倒序要加上descending
var q4 = names.OrderBy(a => a).Where(a=>a.StartsWith("W"));//直接排序
var q5 = names.OrderByDescending(a => a).Where(a=>a.StartsWith("W"));//直接倒序排序

var q6 = from a in names
select new
{
HI = a + ",您好！"
};//查询后重构输出

var q7 = names.Select(a => new { HI = a + ",您好！" });//直接查询构造输出

List<Person> persons = new List<Person>();
persons.Add(new Person() { ID="0001",Name="Kingtiger" });
persons.Add(new Person() { ID = "0002", Name = "Wang" });
persons.Add(new Person() { ID = "0001", Name = "Biao" });
persons.Add(new Person() { ID = "0004", Name = "WangBiao" });

var q8 = from p in persons
orderby p.ID, p.Name
select p;//多级排序，先排序ID，然后再排序Name
var q9 = persons.OrderBy(a => a.ID).ThenBy(a => a.Name).Select(a => a);//直接两个排序

var qt = from p in persons
where p.Name.Contains("W") || p.Name.Contains("Biao")
select p;//第一次查询进行过滤
var q10 = from p in qt
orderby p.Name descending
select p.Name;//对一次查询结果进行第二次处理

var q11 = from p in persons
group p by p.ID into cg
select new {
GroupID = cg.Key,
GroupCount= cg.Count()
};//分组查询，将结果提取出来

List<Order> orders = new List<Order>();
orders.Add(new Order() { UserID="0002",OrderID="001", OrderName="苹果" });
orders.Add(new Order() { UserID = "0002", OrderID = "003", OrderName = "香蕉" });
orders.Add(new Order() { UserID = "0004", OrderID = "002", OrderName = "荔枝" });

var q12 = from p in persons
join o in orders on p.ID equals o.UserID
select new
{
PName = p.Name,
POrderName = o.OrderName
};
foreach (var p in q12)
{
Response.Write(p+"<br/>");
}
}
}

public class Person
{
public string ID { set; get; }
public string Name { set; get; }
}

public class Order
{
public string OrderID { set; get; }
public string OrderName { set; get; }
public string UserID { set; get; }
}