Linq的基本用法，代码

清疚 2022-06-14 09:15 148阅读 0赞

using System;  
using System.Linq;  
using System.Collections.Generic;  
using LinQ;  
  
namespace LinQ  
\{  
    class Program  
    \{  
        static void Main(string\[\] args)  
        \{       
            Console.ReadLine();  
        \}  
  
        \#region Linq语句的语法  
        private static void BasicConcept()  
        \{  
            int\[\] numbers = \{ 5, 10, 8, 3, 6, 12 \};  
            //Linq 语句的两种语法实现  
            //1.Query syntax  
            var numQuery1 = from num in numbers  
                            where num % 2 == 0  
                            orderby num  
                            select num;  
            //2.Method syntax  
            var numQuery2 = numbers.Where(n => n % 2 == 0).OrderBy(n => n);  
  
            foreach (var i in numQuery1)  
            \{  
                Console.WriteLine(i + "");  
            \}  
            Console.WriteLine();  
            foreach (var i in numQuery2)  
            \{  
                Console.WriteLine(i + "");  
            \}  
        \}  
        \#endregion  
  
  
        \#region query 的基本组成 Expamle  
        private static void QuerySyntax()  
        \{  
            //1.data source  
            //必须实现IEnumerble接口  
            int\[\] numbers = \{ 0, 1, 2, 3, 4, 5, 6 \};  
  
            //2.Query creation  
            var numquery = from nums in numbers  
                           where (nums % 2) == 0  
                           select nums;  
  
            //query语句强制执行  
            //int temp = numquery.Count();  
            List<int> list = numquery.ToList<int>();  
            numquery.ToArray<int>();  
  
  
  
            //3.Query execution  
            foreach (var num in numquery)  
            \{  
                Console.WriteLine("\{0,1\}", num);  
            \}  
  
        \}  
        \#endregion  
          
  
        \#region Query语句的基本操作  
        private static void QueyOperation()  
        \{  
            int\[\] numbers = \{ 0, 1, 2, 3, 4, 5, 6, 7 \};  
            var query = from num in numbers  
                        where num % 2 == 1 || num % 3 == 1  
                        orderby num descending  
                        select num;  
            foreach (var num in query)  
            \{  
                Console.WriteLine("\{0\}",num);  
            \}  
  
            List<Customer> customer = new List<Customer>();  
            customer.Add(new Customer() \{ Name = "Jack", City = "Beijing" \});  
            customer.Add(new Customer() \{ Name = "Lilei", City = "Beijing" \});  
            customer.Add(new Customer() \{ Name = "Lili", City = "Shanghai" \});  
  
            List<Employee> employees = new List<Employee>();  
            employees.Add(new Employee()\{Name="Jack",ID=101\});  
            employees.Add(new Employee() \{ Name = "Emily", ID = 102 \});  
  
            var QueryCustomers = from c in customer  
                                 group c by c.City;  
  
            foreach (var cg in QueryCustomers)  
            \{  
                Console.WriteLine(cg.Key);  
                foreach (var c in cg)  
                \{  
                    Console.WriteLine("\{0\}", c.Name);  
                \}  
            \}  
  
  
            var queryjoin = from c in customer  
                            join e in employees on c.Name equals e.Name  
                            select new \{ PersonName = c.Name, PersonID = e.ID, Persioncity = c.City \};  
            foreach (var p in queryjoin)  
            \{  
                Console.WriteLine("\{0\},\{1\},\{2\}", p.PersonName, p.PersonID, p.Persioncity);  
            \}  
  
  
            //Linq的into的使用  
            var QueryCustomers1 = from c in customer  
                                  group c by c.City into cusGroup  
                                  where cusGroup.Count() >= 2  
                                  select new \{ City = cusGroup.Key, Number = cusGroup.Count() \};  
            foreach (var c in QueryCustomers1)  
            \{  
                Console.WriteLine("\{0\} count \{1\}", c.City, c.Number);  
            \}  
  
            //let主要处理中间变量  
            string\[\] strings = \{ "hello hello", "world world", "happy happy" \};  
            var stringQuery = from s in strings  
                              let words = s.Split(' ')  
                              from word in words  
                              let w = word.ToUpper()  
                              select w;  
        \}  
        \#endregion        
          
    \}  
  
  
    class Customer  
    \{  
        public string Name  
        \{  
            get;  
            set;  
        \}  
        public string City  
        \{  
            get;  
            set;  
        \}  
    \}  
  
    class Employee  
    \{  
        public string Name \{ get; set; \}  
        public int ID \{ get; set; \}  
    \}  
\}