C# 3.0新特性初步研究 Part6:使用查询表达式 _C#教程

查询表达式（Query Expression）

大家都应该对SQL语句不陌生吧，在C# 2.0之前，嵌入到代码中的SQL就是下面这个样子：

1public void Test()

2{

3SqlConnection c = new SqlConnection(…);

4 c.Open();

5 SqlCommand cmd = new SqlCommand(

6 @“SELECT c.Name, c.Phone // queries in quotes

7 FROM Customers c

8 WHERE c.City = @p0”

9 );

10 cmd.Parameters[“@po”] = “London”; // arguments loosely bound

11 DataReader dr = c.Execute(cmd);

12 while (dr.Read()) {

13 string name = r.GetString(0);

14 string phone = r.GetString(1); // results loosely typed

15 DateTime date = r.GetDateTime(2); // compiler can’t help catch mistakes

16 }

17 r.Close();

18}

在C# 3.0中，我们可以将“SQL语句”方便的运用到其他地方，当然这里并不是真正的SQL语句~~

我觉得我会在以后的开发过程中使用很多以下的类似代码：

1class Program

2 {

3 static void Main(string[] args)

4 {

5 var contacts = new List<Contact>();

6

7 contacts.Add(new Contact("Michael", "520-331-2718",

8 "33140 SW Liverpool Lane", "WA"));

9 contacts.Add(new Contact("Jennifer", "503-998-1177",

10 "1245 NW Baypony Dr", "OR"));

11 contacts.Add(new Contact("Sean", "515-127-3340",

12 "55217 SW Estate Dr", "WA"));

13

14 var WAContacts =

15 from c in contacts

16 where c.State == "WA"

17 select new { c.Name, c.Phone };

18

19 Console.WriteLine("Contacts in the state of Washington: ");