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：
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：
其中出现的代码：
是否与我们熟悉的SQL语句有着极大的相似性呢？Of Course!
到底是SQL梦见了C#，还是C#梦见了SQL……
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：
1
public void Test()
2
{
3
SqlConnection 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
}
public void Test()2
{
3
SqlConnection c = new SqlConnection(…);4
c.Open(); 5
SqlCommand cmd = new SqlCommand(6
@“SELECT c.Name, c.Phone // queries in quotes7
FROM Customers c8
WHERE c.City = @p0”9
);10
cmd.Parameters[“@po”] = “London”; // arguments loosely bound11
DataReader dr = c.Execute(cmd); 12
while (dr.Read()) {
13
string name = r.GetString(0);14
string phone = r.GetString(1); // results loosely typed15
DateTime date = r.GetDateTime(2); // compiler can’t help catch mistakes16
}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: ");
20![]()
foreach (var c in WAContacts)
21![]()
{
22![]()
Console.WriteLine("Name: {0}, Phone: {1}", c.Name, c.Phone);
23![]()
}
24![]()
}
25![]()
}
26![]()
27![]()
class Contact
28![]()
{
29![]()
public string Name;
30![]()
public string Phone;
31![]()
public string Address;
32![]()
public string State;
33![]()
34![]()
public Contact(string name, string phone, string address, string state)
35![]()
{
36![]()
this.Name = name;
37![]()
this.Phone = phone;
38![]()
this.Address = address;
39![]()
this.State = state;
40![]()
}
41![]()
}
class Program2
{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: ");20
foreach (var c in WAContacts)21
{22
Console.WriteLine("Name: {0}, Phone: {1}", c.Name, c.Phone);23
}24
}25
}26
27
class Contact28
{29
public string Name;30
public string Phone;31
public string Address;32
public string State;33
34
public Contact(string name, string phone, string address, string state)35
{36
this.Name = name;37
this.Phone = phone;38
this.Address = address;39
this.State = state;40
}41
}其中出现的代码：
1![]()
var WAContacts =
2![]()
from c in contacts
3![]()
where c.State == "WA"
4![]()
select new { c.Name, c.Phone };
var WAContacts =2
from c in contacts 3
where c.State == "WA" 4
select new { c.Name, c.Phone };是否与我们熟悉的SQL语句有着极大的相似性呢？Of Course!
到底是SQL梦见了C#，还是C#梦见了SQL……
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