初学.net遇到的问题：数据库访问连接问题

错误一：运行代码时出现如下错误：

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编译器错误信息: BC30002: 未定义类型“ADOConnection”。

源错误:

行 11： <Script Language="VB" Runat="Server">

行 12： Sub Button1_Click(sender As Object, E As EventArgs)

行 13： Dim cnA As ADOConnection=New ADOConnection

行 14： Dim cmA As ADOCommand=New ADOCommand

行 15： cnA.Provider="Microsoft.Jet.OLEDB.4.0"

源文件: g:\inetpub\wwwroot\WebApplication1\WebForm3.aspx 行: 13

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这是因为NameSpace出错！

使用如下：

<%@ import Namespace="system.data" %>

<%@ import Namespace="system.data.Oledb" %>

对应变量声明为：

dim myconn as OledbConnection

dim mycommand as OledbCommand

<%@ import Namespace="system.data" %>

<%@ import Namespace="system.data.SqlClient" %>

对应变量声明为：

dim myconn as SqlConnection

dim mycommand as SqlCommand

<%@ import Namespace="system.data" %>

<%@ import Namespace="system.data.ODBC" %>

对应变量声明为：

dim myconn as ODBCConnection

dim mycommand as ODBCCommand

测试程序分别如下：

=============================

<%@ import Namespace="system.data" %>

<%@ import Namespace="system.data.Oledb" %>

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">

<HTML>

<HEAD>

<title>WebForm1</title>

</HEAD>

<BODY>

Sub Page_load(Sender As Object, E As EventArgs)

dim ds as dataset

dim myconn as OledbConnection

dim mycommand as OledbCommand

myconn=new Oledbconnection("Provider=SQLOLEDB; Data Source=(local);uid=sa; pwd=pssword; Initial Catalog=database")

myconn.open()

mycommand=new Oledbcommand("select * from user_info",myconn)

Dim myReader As OleDbDataReader = myCommand.ExecuteReader(CommandBehavior.CloseConnection)

Datagrid1.DataSource =myreader

Datagrid1.DataBind()

End Sub

</script>

<P>

<asp:datagrid id="DataGrid1" runat="server"></asp:datagrid></FONT>

</P>

</BODY>

</HTML>

==============================

<%@ import Namespace="system.data" %>

<%@ import Namespace="system.data.SqlClient" %>

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">

<HTML>

<HEAD>

<title>WebForm1</title>

</HEAD>

<BODY>

Sub Page_load(Sender As Object, E As EventArgs)

dim ds as dataset

dim myconn as sqlconnection

dim mycommand as SqlCommand

myconn=new Sqlconnection("server=(local); uid=sa; pwd=huangfeng;database=jxjyzb")

myconn.open()

mycommand=new Sqlcommand("select * from user_info",myconn)

Dim myReader As SqlDataReader = myCommand.ExecuteReader(CommandBehavior.CloseConnection)

Datagrid1.DataSource =myreader

Datagrid1.DataBind()

End Sub

</script>

<P>

<asp:datagrid id="DataGrid1" runat="server"></asp:datagrid></FONT>

</P>

</BODY>

</HTML>

==============================

<%@ import Namespace="system.data" %>

<%@ import Namespace="system.data.ODBC" %>

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">

<HTML>

<HEAD>

<title>WebForm1</title>

</HEAD>

<BODY>

Sub Page_load(Sender As Object, E As EventArgs)

dim ds as dataset

dim myconn as Odbcconnection

dim mycommand as OdbcCommand

myconn=new ODbcconnection("DRIVER={SQL Server};uid=yourusername;pwd=yourpassword;SERVER=(local);DATABASE=yourdatabasename")

myconn.open()

mycommand=new ODBCcommand("select * from user_info",myconn)

Dim myReader As ODBCDataReader = myCommand.ExecuteReader(CommandBehavior.CloseConnection)

Datagrid1.DataSource =myreader

Datagrid1.DataBind()

End Sub

</script>

<P>

<asp:datagrid id="DataGrid1" runat="server"></asp:datagrid></FONT>

</P>

</BODY>

</HTML>

==============================

以上程序编写各类和方法的使用可参考：

http://msdn.microsoft.com/library/chs/default.asp?url=/library/CHS/cpref/html/frlrfsystemdataoledboledbcommandmemberstopic.asp

注意在使用数据库连接时，应对应使用不同种的格式字符串连接：

如果您使用凭据（用户名和密码）来连接到 SQL Server 数据库，则连接字符串形式如下：

Using the SQL Server .NET Data Provider:

SqlConnection conn = new SqlConnection(

"server=YourServer; uid=YourUserName; pwd=YourStrongPwd;" +

"database=YourDatabase");

Using the OLE DB .NET Data Provider:

OleDbConnection conn = new OleDbConnection(

"Provider=SQLOLEDB; Data Source=YourServer;" +

"uid=YourUserName; pwd=YourStrongPwd; Initial Catalog=YourDatabase");

Using the ODBC .NET Data Provider:

ODBCConnection conn = new ODBCConnection(

"DRIVER={SQL Server};SERVER=MyServer;uid=YourUserName; pwd=YourStrongPwd;DATABASE=northwind;");

如果您需要连接到安装在同一计算机上的 SQL Server 的特定实例（只在 SQL Server 2000 或以后版本中提供的功能），则连接字符串形式如下：

Using the SQL Server .NET Data Provider:

SqlConnection conn = new SqlConnection(

"server=YourServer\Instance; uid=YourUserName; pwd=YourStrongPwd;" +

"database=YourDatabase");

如果您利用显式凭据（用户名和密码）连接到 Oracle 数据库，则连接字符串形式如下：

OleDbConnection conn = new OleDbConnection(

"Provider=MSDAORA; Data Source=YourDatabaseAlias;" +

"User ID=YourUserName; Password=YourStrongPwd;");

以上我查了好多网上下载的CHM帮助文件，测试源程序，都测试出现类似错误。仔细查阅微软在线帮助，发现System.Date.Sql在新版本的.Net框架中已经不再使用了，这点值得新手注意。

数据安全访问设计详细参考如下：http://www.microsoft.com/china/msdn/library/architecture/architecture/architecturetopic/BuildSucApp/BSAAsecmod12.mspx