C#Linq

Main

static void Main(string[] args)
        {
            BasicConcept();

            QuerySyntax();

            QueryOperations();
            Console.ReadLine();
        }

1、Query Syntax、Method Syntax

private static void BasicConcept()
        {
            int[] numbers = { 5, 10, 8, 3, 6, 12 };
            //1、Query syntax
            var numQuery1 = from num in numbers
                            where num % 2 == 0
                            orderby num
                            select num;
            foreach (var i in numQuery1)
            {
                Console.Write(i + " ");
            }
            Console.WriteLine();
            //2、Method syntax
            var numQuery2 = numbers.Where(p => p % 2 == 0).OrderBy(p => p);
            foreach (var i in numQuery2)
            {
                Console.Write(i + " ");
            }
        }

2、Query Syntax语法

private static void QuerySyntax()
        {
            //1、Data Source
            int[] numbers = { 0, 1, 2, 3, 4, 5, 6 };

            //2、Query creation
            var numQuery = from num in numbers
                           where num % 2 == 0
                           select num;

            //3、Query execution
            foreach (var num in numQuery)
            {
                Console.Write("{0,1} ", num);
            }
        }

3、关键字group by、join、let、into

private static void QueryOperations()
        {
            List<Customer> custorms = new List<Customer>();
            custorms.Add(new Customer() { Name = "Jack", City = "Beijing" });
            custorms.Add(new Customer() { Name = "Joy", City = "Beijing" });
            custorms.Add(new Customer() { Name = "Tom", City = "Shanghai" });

            List<Employee> employees = new List<Employee>();
            employees.Add(new Employee() { Name = "Jack", ID = 101 });
            employees.Add(new Employee() { Name = "Jackson", ID = 102 });

            var query = from c in custorms
                        group c by c.City into cusGroup
                        where cusGroup.Count() >= 2
                        select new { City = cusGroup.Key, Number = cusGroup.Count() };

            //foreach (var cg in query)
            //{
            //    Console.WriteLine(cg.Key);
            //    foreach (var c in cg)
            //    {
            //        Console.WriteLine(" {0}", c.Name);
            //    }
            //}

            foreach (var c in query)
            {
                Console.WriteLine("{0} Count {1}", c.City, c.Number);
            }

            var queryJoin = from c in custorms
                            join e in employees on c.Name equals e.Name
                            select new { PersonName = c.Name, PersonID = e.ID, PersonCity = c.City };

            foreach (var p in queryJoin)
            {
                Console.WriteLine("{0} {1} {2}", p.PersonName, p.PersonID, p.PersonCity);
            }

            string[] strings = { "Hello World", "This is Friday", "Are you happy?" };
            var stringQuery = from s in strings
                              let words = s.Split(' ')
                              from word in words
                              let w = word.ToUpper()
                              select w;
            foreach (var s in stringQuery)
            {
                Console.Write(s + " ");
            }
        }
class Customer
        {
            public string Name
            {
                get;
                set;
            }
            public string City
            {
                get;
                set;
            }
        }

        class Employee
        {
            public string Name { get; set; }
            public int ID { get; set; }
        }