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初学.net遇到的问题：数据库访问连接问题

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错误一：运行代码时出现如下错误：
-------------------------------------------------------------------
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
-----------------------------------------------------------------------------
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>
<script language="vb" runat="server">
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>
<meta content="Microsoft Visual Studio .NET 7.1" name="GENERATOR">
<FONT face="宋体">
<asp:datagrid id="DataGrid1" runat="server"></asp:datagrid></FONT>
<meta content="Visual Basic .NET 7.1" name="CODE_LANGUAGE">
<meta content="JavaScript" name="vs_defaultClientScript">
<meta content="http://schemas.microsoft.com/intellisense/ie5" name="vs_targetSchema">
</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>
<script language="vb" runat="server">
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>
<meta content="Microsoft Visual Studio .NET 7.1" name="GENERATOR">
<FONT face="宋体">
<asp:datagrid id="DataGrid1" runat="server"></asp:datagrid></FONT>
<meta content="Visual Basic .NET 7.1" name="CODE_LANGUAGE">
<meta content="JavaScript" name="vs_defaultClientScript">
<meta content="http://schemas.microsoft.com/intellisense/ie5" name="vs_targetSchema">
</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>
<script language="vb" runat="server">
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>
<meta content="Microsoft Visual Studio .NET 7.1" name="GENERATOR">
<FONT face="宋体">
<asp:datagrid id="DataGrid1" runat="server"></asp:datagrid></FONT>
<meta content="Visual Basic .NET 7.1" name="CODE_LANGUAGE">
<meta content="JavaScript" name="vs_defaultClientScript">
<meta content="http://schemas.microsoft.com/intellisense/ie5" name="vs_targetSchema">
</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


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