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; }
}