LinQ综合应用实例

     直接上代码，内容很浅显易懂，在这里就不做更多的解释，解释见代码注释。

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; }

}