C#Linq

Main

1 static void Main(string[] args)
2         {
3             BasicConcept();
4 
5             QuerySyntax();
6 
7             QueryOperations();
8             Console.ReadLine();
9         }

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1、Query Syntax、Method Syntax

 1 private static void BasicConcept()
 2         {
 3             int[] numbers = { 5, 10, 8, 3, 6, 12 };
 4             //1、Query syntax
 5             var numQuery1 = from num in numbers
 6                             where num % 2 == 0
 7                             orderby num
 8                             select num;
 9             foreach (var i in numQuery1)
10             {
11                 Console.Write(i + " ");
12             }
13             Console.WriteLine();
14             //2、Method syntax
15             var numQuery2 = numbers.Where(p => p % 2 == 0).OrderBy(p => p);
16             foreach (var i in numQuery2)
17             {
18                 Console.Write(i + " ");
19             }
20         }

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2、Query Syntax语法

 1 private static void QuerySyntax()
 2         {
 3             //1、Data Source
 4             int[] numbers = { 0, 1, 2, 3, 4, 5, 6 };
 5 
 6             //2、Query creation
 7             var numQuery = from num in numbers
 8                            where num % 2 == 0
 9                            select num;
10 
11             //3、Query execution
12             foreach (var num in numQuery)
13             {
14                 Console.Write("{0,1} ", num);
15             }
16         }

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3、关键字group by、join、let、into

 1 private static void QueryOperations()
 2         {
 3             List<Customer> custorms = new List<Customer>();
 4             custorms.Add(new Customer() { Name = "Jack", City = "Beijing" });
 5             custorms.Add(new Customer() { Name = "Joy", City = "Beijing" });
 6             custorms.Add(new Customer() { Name = "Tom", City = "Shanghai" });
 7 
 8             List<Employee> employees = new List<Employee>();
 9             employees.Add(new Employee() { Name = "Jack", ID = 101 });
10             employees.Add(new Employee() { Name = "Jackson", ID = 102 });
11 
12             var query = from c in custorms
13                         group c by c.City into cusGroup
14                         where cusGroup.Count() >= 2
15                         select new { City = cusGroup.Key, Number = cusGroup.Count() };
16 
17             //foreach (var cg in query)
18             //{
19             //    Console.WriteLine(cg.Key);
20             //    foreach (var c in cg)
21             //    {
22             //        Console.WriteLine(" {0}", c.Name);
23             //    }
24             //}
25 
26             foreach (var c in query)
27             {
28                 Console.WriteLine("{0} Count {1}", c.City, c.Number);
29             }
30 
31             var queryJoin = from c in custorms
32                             join e in employees on c.Name equals e.Name
33                             select new { PersonName = c.Name, PersonID = e.ID, PersonCity = c.City };
34 
35             foreach (var p in queryJoin)
36             {
37                 Console.WriteLine("{0} {1} {2}", p.PersonName, p.PersonID, p.PersonCity);
38             }
39 
40             string[] strings = { "Hello World", "This is Friday", "Are you happy?" };
41             var stringQuery = from s in strings
42                               let words = s.Split(' ')
43                               from word in words
44                               let w = word.ToUpper()
45                               select w;
46             foreach (var s in stringQuery)
47             {
48                 Console.Write(s + " ");
49             }
50         }
51 class Customer
52         {
53             public string Name
54             {
55                 get;
56                 set;
57             }
58             public string City
59             {
60                 get;
61                 set;
62             }
63         }
64 
65         class Employee
66         {
67             public string Name { get; set; }
68             public int ID { get; set; }
69         }

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