C#中匿名委托以及Lambda表达式的学习笔记

2018-06-23 23:42:09来源：未知阅读 ()

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

 1 int[] nums = { 5, 4, 1, 3, 9, 8, 6, 7, 2, 0 };
 2             IEnumerable<int> newNums = from n in nums where n > 0 select n;
 3             newNums = newNums.Where(new Func<int,int, bool>(delegate(int i,int index) { return i < index; }));
 4             newNums = newNums.Where(new Func<int, int, bool>((int i, int index)=> i < index));
 5             newNums = newNums.Where(delegate(int i, int index) { return i < index; });
 6             newNums = newNums.Where((i, index) => i < index);
 7             foreach (var i in newNums)
 8             {
 9                 Console.WriteLine(i);
10             }

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

 1     public class Store
 2     {
 3         public string Id;
 4         public string Name;
 5     }
 6     public class Person
 7     {
 8         public string name { get; set; }
 9         public int age { get; set; }
10         public string StoreId { get; set; }
11     }

2.插入数据

 1             var Stores = new List<Store>()
 2             {
 3                 new Store() { Id="1",Name="1班"},
 4                 new Store() { Id="2",Name="2班"}
 5             };
 6 
 7             var Persons = new List<Person>()
 8             {
 9                 new Person() { name="p1",age=1, StoreId="1"},
10                 new Person() { name="p2",age=2, StoreId="1"},
11                 new Person() { name="p3",age=3, StoreId="1"},
12                 new Person() { name="p4",age=4, StoreId="2"},
13                 new Person() { name="p5",age=5, StoreId="1"},
14                 new Person() { name="p6",age=6, StoreId="2"},
15                 new Person() { name="p7",age=7, StoreId="1"},
16                 new Person() { name="p8",age=8, StoreId="1"}
17             };

3. 查询年龄小于3岁的人1班和2班分别有几个人

1             var plst = Persons.Where(o => o.age > 3).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 });
2             foreach (var p in plst)
3             {
4                 Console.WriteLine(p.storeName + "有" + p.Count + "个人");
5             }