LINQ(语言集成查询)使用案例

using System; using System.Collections.Generic; using System.Linq; using System.Text; using System.Threading.Tasks; namespace LinkConsole { class Program { static void Main(string[] args) { //-------------最基本的简单查询----------------// List numbers = new List() { 1,2,3,4,5,6,7,8,9,10}; var numQuery = from num in numbers where num % 2 == 0 select num; foreach (var num in numQuery) { Console.WriteLine("{0,1}", num); } //-------------读取List<>中的句子----------------// FormExpDemo2(); //-------------复合form子句----------------// FormExpDemo(); //-------------多个from句子---------------// FormExpDemo3(); //-------------where-------------------// WhereExpDemo(); //-------------select------------------// SelectDemo(); //-------------group--------------------// GroupDemo(); //-------------into------------------------// IntoDemo(); //--------------OrderBy--------------------// ThenByDemo(); //--------------let----------------------// LetDemo(); //--------------join--------------------// JoinDemo(); Console.ReadLine(); } public class CustomerInfo { public string Name { get; set; } public int Age { get; set; } public string Tel { get; set; } public List telTable { get; set; } } public static void FormExpDemo2() { // List customers = new List { new CustomerInfo{ Name = "欧阳晓晓",Age = 35,Tel = "123"}, new CustomerInfo{ Name = "上官飘飘",Age = 17,Tel = "456"}, new CustomerInfo{ Name = "诸葛菲菲",Age = 23,Tel = "789"} }; var query = from ci in customers where ci.Age > 20 select ci; foreach (var ci in query) { Console.WriteLine("姓名：{0}年龄：{1}电话：{2}", ci.Name, ci.Age, ci.Tel); } } //复合from子句    // 相当于两个for循环而已 private static void FormExpDemo() { List customers = new List { new CustomerInfo { Name = "欧阳小小",Age= 35,telTable = new List {"123","234"} }, new CustomerInfo { Name = "上官飘飘",Age= 35,telTable = new List {"456","567"} }, new CustomerInfo { Name = "诸葛菲菲",Age= 35,telTable = new List {"789","456"} }, }; //查询包含电话号码456的客户 var query = from ci in customers from tel in ci.telTable where tel.IndexOf("456") > -1 select ci; foreach (var ci in query) { Console.WriteLine("姓名：{0}年龄：{1}", ci.Name, ci.Age); foreach (var tel in ci.telTable) { Console.WriteLine("          电话：{0}", tel); } } } //多个from子句，和复合子句看起来是一样的，其实不一样，一个是单个数据源中的子元素的集合，一个是对多个数据源进行查询 private static void FormExpDemo3() { List customers = new List { new CustomerInfo{ Name = "欧阳晓晓",Age = 35,Tel = "123"}, new CustomerInfo{ Name = "上官飘飘",Age = 77,Tel = "456"}, new CustomerInfo{ Name = "诸葛菲菲",Age = 23,Tel = "789"} }; List customers2 = new List { new CustomerInfo{ Name = "令狐冲",Age = 25,Tel = "123"}, new CustomerInfo{ Name = "东方不败",Age = 15,Tel = "456"}, new CustomerInfo{ Name = "任盈盈",Age = 13,Tel = "789"} }; //在customers 中寻找年龄大于20的客户 //在customenrs中寻找年龄小于30岁的客户 var query = from custo in customers where custo.Age > 20 from custo2 in customers2 where custo2.Age <30 select new { custo, custo2 }; foreach (var ci in query) console.writeline("{0},{1}", ci.custo.name, ci.custo2.name);> clist = new List { new CustomerInfo{ Name="欧阳晓晓", Age=35, Tel ="1330708****"}, new CustomerInfo{ Name="上官飘飘", Age=17, Tel ="1592842****"}, new CustomerInfo{ Name="令狐冲", Age=23, Tel ="1380524****"} }; //可以查询符合多个条件的人(名字是三个字或者姓令的，但年龄必须大于20) var query = from custo in clist where (custo.Name.Length == 3 || custo.Name.Substring(0, 1) == "令") && custo.Age > 20 select custo;//select 也可以改成，比如custo.Name。或者用一个函数，把变量传出去 foreach (var ci in query) { Console.WriteLine("姓名：{0}年龄：{1}电话：{2}", ci.Name, ci.Age, ci.Tel); } //where中使用自定义函数,查询三个字并且姓令的客户 var query2 = from custo in clist where (custo.Name.Length == 3 && ChechName(custo.Name)) select custo; foreach (var ci in query2) { Console.WriteLine("姓名：{0}年龄：{1}电话：{2}", ci.Name, ci.Age, ci.Tel); } } private static bool ChechName(string name) { if (name.Substring(0, 1) == "令") return true; else return false; } //select 用法举例 private static void SelectDemo() { List clist = new List { new CustomerInfo{ Name="欧阳晓晓", Age=35, Tel ="1330708****"}, new CustomerInfo{ Name="上官飘飘", Age=17, Tel ="1592842****"}, new CustomerInfo{ Name="令狐冲", Age=23, Tel ="1380524****"} }; string[] names = { "令狐冲", "任盈盈", "杨过", "小龙女", "欧阳小夏", "欧阳晓晓" }; //查询在给定谓词数组里存在的客户 var query = from custo in clist where custo.Age <30 select new mycustomerinfo { name tel }; foreach (var ci in query) console.writeline("姓名：{0}电话：{1}类型{2}", ci.name, ci.tel, ci.gettype().fullname); } public class string get; set;> clist = new List { new CustomerInfo{ Name="欧阳晓晓", Age=35, Tel ="1330708"}, new CustomerInfo{ Name="上官飘飘", Age=17, Tel ="1592842"}, new CustomerInfo{ Name="欧阳锦鹏", Age=35, Tel ="1330708"}, new CustomerInfo{ Name="上官无忌", Age=23, Tel ="1380524"} }; private static void GroupDemo() { //按照名字的前两个字进行分组 var query = from custo in clist group custo by custo.Name.Substring(0, 2); foreach (IGrouping group in query) { Console.WriteLine("分组键：{0}", group.Key); foreach (var ci in group) { Console.WriteLine("姓名：{0}电话：{1}", ci.Name, ci.Tel); } Console.WriteLine("*********************"); } //可以知道group子句返回的是一个IGrouping泛型接口的对象集合 //TKey是键的对象类型，在用于group子句的时候，编译器会识别数据类型，用于存储分组的键值,也就是根据什么分的组 //TElement是指的对象类型用于分配储存结果，变量基于这个接口的类型就是遍历这个值，也就是分组的对象 } //----------------into子句---------------// private static void IntoDemo() { //into提供了一个临时标识符，它储存了into子句前面的查询内容，使他后面的子句可以方便使用，再次查询投影 var query = from custo in clist group custo by custo.Name.Substring(0, 2) into gpcustomer orderby gpcustomer.Key descending //排序， select gpcustomer; Console.WriteLine("into用于group子句"); foreach (var group in query) { Console.WriteLine("分组见：{0}", group.Key); foreach (var ci in group) { Console.WriteLine("姓名：{0}电话：{1}", ci.Name, ci.Tel); } Console.WriteLine("***********************"); } var query2 = from custo in clist select new { NewName = custo.Name, NewAge = custo.Age } into newCustomer orderby newCustomer.NewAge select newCustomer; Console.WriteLine("into用于select子句"); foreach (var ci in query2) { Console.WriteLine("{0}年龄：{1}", ci.NewName, ci.NewAge); } } //---------------排序子句--------------------// //LINQ可以按元素的一个或者多个属性对元素进行排序，表达式的排序方式分为OrderBy、OrderByDescending、ThenBy、ThenByDescending //加了Descending的就是降序，没有加的就是升序 private static void ThenByDemo() { List clist = new List { new CustomerInfo{ Name="欧阳晓晓 ", Age=35, Tel ="1330708****"}, new CustomerInfo{ Name="上官飘飘 ", Age=17, Tel ="1592842****"}, new CustomerInfo{ Name="郭靖 ", Age=17, Tel ="1330708****"}, new CustomerInfo{ Name="黄蓉 ", Age=17, Tel ="1300524****"} }; //按照年龄升序，再按照名字的字数次要排序 var query = from customer in clist orderby customer.Age, customer.Name.Length select customer; Console.WriteLine("按年龄排列，按名字字数进行次要排序"); foreach (var ci in query) { Console.WriteLine("姓名:{0} 年龄：{1} 电话：{2}",ci.Name, ci.Age, ci.Tel); } //按年龄降序，再按名字的字数降序次要排列 var query2 = from customer in clist orderby customer.Age descending , customer.Name.Length descending select customer; Console.WriteLine("\n按年龄排列，按名字字数进行降序次要排列"); foreach (var ci in query2) { Console.WriteLine("姓名：{0} 年龄：{1} 电话：{2}", ci.Name, ci.Age, ci.Tel); } } //--------------let子句---------------------// private static void LetDemo() { var query = from custo in clist let g = custo.Name.Substring(0, 1)//let建立一个范围变量，在where中使用 where g == "欧" || g == "上"//也可以不写，写成customer.Name.Substring(0, 1) == "郭" || customer.Name.Substring(0, 1) == "黄" select custo; foreach (var ci in query) { Console.WriteLine("姓名：{0} 年龄：{1} 电话：{2}", ci.Name, ci.Age, ci.Tel); } } //-------------join子句-------------------// private static void JoinDemo() { //如果两个数据源中的属性可以进行相等比较，那么两个句子可以用join进行关联，比较的符号为equal，而不是== List clist = new List { new CustomerInfo{ Name="欧阳晓晓", Age=35, Tel ="1330708****"}, new CustomerInfo{ Name="上官飘飘", Age=17, Tel ="1592842****"}, new CustomerInfo{ Name="郭靖", Age=17, Tel ="1330708****"}, new CustomerInfo{ Name="黄蓉", Age=17, Tel ="1300524****"} }; List titleList = new List { new CustomerTitle{ Name="欧阳晓晓", Title="歌手"}, new CustomerTitle{ Name="郭靖", Title="大侠"}, new CustomerTitle{ Name="郭靖", Title="洪七公徒弟"}, new CustomerTitle{ Name="黄蓉", Title="才女"}, new CustomerTitle{ Name="黄蓉", Title="丐帮帮主"} }; //根据姓名进行内部联结 var query = from customer in clist join title in titleList on customer.Name equals title.Name select new { Name = customer.Name, Age = customer.Age, Title = title.Title }; foreach (var ci in query) { Console.WriteLine("姓名：{0} 年龄：{1}{2}", ci.Name, ci.Age, ci.Title); } //根据姓名进行分组联结 Console.WriteLine("\n根据姓名进行分组联结"); var query2 = from customer in clist join title in titleList on customer.Name equals title.Name into tgroup select new { Name = customer.Name, Titles = tgroup }; foreach (var g in query2) { Console.WriteLine(g.Name); foreach (var g2 in g.Titles) { Console.WriteLine("     {0}", g2.Title); } } //根据姓名进行 左外部联结 Console.WriteLine("\n左外部联结"); var query3 = from customer in clist join title in titleList on customer.Name equals title.Name into tgroup from subTitle in tgroup.DefaultIfEmpty() select new { Name = customer.Name, Title = (subTitle == null ? "空缺" : subTitle.Title) }; foreach (var ci in query3) { Console.WriteLine("姓名：{0} ", ci.Name, ci.Title); } } public class CustomerTitle { public string Name { get; set; } public string Title { get; set; } } } }