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 }
4.输出
2班有2个人
1班有3个人
