C# LINQ

1. 自定义 Master，Kongfu 类

class Master
{

    public int Id { get; set; }
    public string Name { get; set; }
    public int Age { get; set; }
    public string MenPai { get; set; }
    public string Kongfu { get; set; }
    public int Level { get; set; }

    public override string ToString()
    {
        return string.Format("Id:{0},Name:{1},Age:{2},MenPai:{3},Kongfu:{4},Level:{5}", Id, Name, Age,MenPai,Kongfu,Level);
    }
}

class Kongfu
{
    public int Id { get; set; }
    public string Name { get; set; }
    public int Power { get; set; }

    public override string ToString()
    {
        return string.Format("Id:{0},Name:{1},Power:{2}", Id, Name, Power);
    }
}

2. 测试代码

class Program
{
    static void Main(string[] args)
    {
        var master = new List<Master>()
        {
            new Master() { Id = 100, Age = 100, Kongfu = "九阳神功",Level=10,MenPai="华山",Name="李二狗" },
            new Master() { Id = 50, Age = 10, Kongfu = "九阳神功1" ,Level=5,MenPai="华山",Name="李大狗"},
            new Master() { Id = 200, Age = 60, Kongfu = "九阳神功2",Level=6,MenPai="华山",Name="李狗蛋" },
        };

        var kongfu = new List<Kongfu>()
        {
            new Kongfu(){Id=1,Name="打狗棒法",Power=90},
            new Kongfu(){Id=2,Name="打狗棒法1",Power=30},
            new Kongfu(){Id=3,Name="打狗棒法2",Power=20},
        };
          
        //使用LINQ做查询（表达式写法）
        var res1 = from m in master   //from后面设置查询的集合
                    where m.Level > 8     //where跟上条件

                    select m;//表示m的结果
        //select m.Name;  //只输出名字

      
        //多个条件
        var res3 = from m in master

                    where m.Level > 8 && m.MenPai == "丐帮"

                    select m;

        var res4 = master.Where(m => m.Level > 8 && m.MenPai == "丐帮");

        //LINQ联合查询
        var res5 = from m in master
                    from k in kongfu
                    where m.Kongfu==k.Name
                    select new { master = m, kongfu = k };
                    //select m;
        foreach (var temp in res)
        {
            Console.WriteLine(temp);
        }

        //join on 联合查询
        var res12 = from m in master
                    join k in kongfu on m.Kongfu equals k.Name
                    where k.Power>90
                    select new { master = m, kongfu = k };


        //对查询结果升序排序
        var res7 = from m in master

                    where m.Level > 8 && m.MenPai == "丐帮"
                    orderby m.Age

                    select m;

        //对查询结果倒序排序
        var res8 = from m in master

                    where m.Level > 8 && m.MenPai == "丐帮"
                    orderby m.Age descending

                    select m;

        //对查询结果升序排序
        var res9 = from m in master

                    where m.Level > 8 && m.MenPai == "丐帮"
                    orderby m.Age,m.Level //按照多个字段进行排序，如果字段的属性相同，就按照第二个属性排序

                    select m;

        var res10 = master.Where(m => m.Level > 8 && m.MenPai == "丐帮").OrderBy(m => m.Age);
        var res11 = master.Where(m => m.Level > 8 && m.MenPai == "丐帮").OrderBy(m => m.Age).ThenBy(m=>m.Level);



        //把人物按照所学功夫进行分类，看下哪个功夫修炼人数最多(分组查询)
        var res13 = from k in kongfu
                    join m in master on k.Name equals m.Kongfu
                    into groups
                    orderby groups.Count()
                    select new { kongfu = k,count=groups.Count()};

        //按照字段分组
        var res14 = from m in master
                    group m by m.MenPai
                    into g
                    select new { count=g.Count(),key=g.Key}; //g.Key按照哪个属性分组

        //量词操作符any all判断集合中是否满足某个条件
        bool res15=master.Any(m => m.MenPai == "丐帮");
        Console.WriteLine(res15);//只要有一个满足返回true

        bool res16=master.All(m => m.MenPai == "丐帮");//所有都满足才返回true



        Console.ReadKey();
    }

    //过滤方法
    static bool Test1(Master m)
    {
        if (m.Level > 8) return true;
        return false;
    }
}