C#中匿名委托以及Lambda表达式的学习笔记

一. C#从1.0到4.0, 随着Linq,泛型的支持，代码越来越简单优雅

 int[] nums = { , , , , , , , , ,  };
             IEnumerable<int> newNums = from n in nums where n >  select n;
             newNums = newNums.Where(new Func<int,int, bool>(delegate(int i,int index) { return i < index; }));
             newNums = newNums.Where(new Func<int, int, bool>((int i, int index)=> i < index));
             newNums = newNums.Where(delegate(int i, int index) { return i < index; });
             newNums = newNums.Where((i, index) => i < index);
             foreach (var i in newNums)
             {
                 Console.WriteLine(i);
             }

二.集合操作，也可适于到EF的数据库操作

1.创建两个实体类

     public class Store
     {
         public string Id;
         public string Name;
     }
     public class Person
     {
         public string name { get; set; }
         public int age { get; set; }
         public string StoreId { get; set; }
     }

2.插入数据

             var Stores = new List<Store>()
             {
                 new Store() { Id="",Name="1班"},
                 new Store() { Id="",Name="2班"}
             };

             var Persons = new List<Person>()
             {
                 new Person() { name="p1",age=, StoreId=""},
                 new Person() { name="p2",age=, StoreId=""},
                 new Person() { name="p3",age=, StoreId=""},
                 new Person() { name="p4",age=, StoreId=""},
                 new Person() { name="p5",age=, StoreId=""},
                 new Person() { name="p6",age=, StoreId=""},
                 new Person() { name="p7",age=, StoreId=""},
                 new Person() { name="p8",age=, StoreId=""}
             };

3. 查询年龄小于3岁的人1班和2班分别有几个人

             var plst = Persons.Where(o => o.age > ).GroupBy(o => o.StoreId).Select(g => new { StoreId = g.Key, Count = g.Count() }).Join(Stores, s => s.StoreId, p => p.Id, (s, p) => new { s.StoreId, storeName = p.Name, s.Count });
             foreach (var p in plst)
             {
                 Console.WriteLine(p.storeName + "有" + p.Count + "个人");
             }

4.输出

2班有2个人
1班有3个人