用C#实现用户名登录---连接数据库,查询并判断是否存在用户名
一、链接类
1.添加DBConnection类
2构造
public class DBConnection
{
private static string _ConnectionString = null; public static SqlConnection Connection
{
get
{
//从配置文件中读取链接字符串
_ConnectionString = ConfigurationManager.ConnectionStrings["mydb"].ConnectionString;
//使 用链接字符串构建接对象
SqlConnection conn = new SqlConnection(_ConnectionString);
return conn;
}
}
}
(也可以在get{}中定义一个string变量接收configuration)
public class DBConnection
{
public static SqlConnection Connection
{
get
{
//从配置文件中读取链接字符串
string _ConnectionString = ConfigurationManager.ConnectionStrings["mydb"].ConnectionString;
//使 用链接字符串构建接对象
SqlConnection conn = new SqlConnection(_ConnectionString);
return conn;
}
}
}
二、添加配置文件
1.引用右键添加system.configuration引用
2.添加新建项--应用程序配置文件
3.APP.config
<connectionStrings>
<add name="mydb" connectionString="server=.;database=mydb;uid=sa;pwd=123"/>
</connectionStrings>
//注意:配置文件中name名要与DBConnection类中ConnectionString[""]中的字段一样
三、打开关闭数据库
1.Main函数调用DBConnection类里面的Connection属性
class Program
{
static void Main(string[] args)
{
SqlConnection conn = DBConnection.Connection;
Console.WriteLine(conn.State);
conn.Open();
Console.WriteLine(conn.State);
conn.Close();
Console.WriteLine(conn.State);
}
}
执行结果