HOW TO: Build a Connection String Programmatically in ADO.NET by Using Visual C++ .NET (310084)

SUMMARY

This step-by-step article describes how to use the Data Link Properties dialog box to programmatically create a connection string at design time.

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Requirements

The following list outlines the recommended hardware, software, network infrastructure, and service packs that you need:

• Microsoft Windows 2000 Professional, Windows 2000 Server, Windows 2000 Advanced Server, or Windows NT 4.0 Server
• Microsoft Visual Studio .NET

This article assumes that you are familiar with the following topics:

• Visual Studio .NET
• ADO.NET fundamentals and syntax
• ActiveX Data Objects (ADO) fundamentals and syntax

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Create an ADO Connection

1. Start Visual Studio .NET and create a new Managed C++ Application. Name it CreateDL.
2. Replace the default code in CreateDL.cpp with the following code:

   #include "stdafx.h"
   #include <stdio.h>
   
   #undef EOF
   #import "c:\program files\common files\system\ole db\oledb32.dll" rename_namespace("dlinks")
   #import "c:\program files\common files\system\ado\msado15.dll" rename_namespace("ado")
   
   void TestConnection(void);
   
   #ifdef _UNICODE
   int wmain(void)
   #else
   int main(void)
   #endif
   {
       TestConnection();
       return 0;
   }
   
   void TestConnection(void)
   {
   	using namespace dlinks;
   	using namespace ado;
   	
   	HRESULT hr;
      	::CoInitialize( NULL );
      	IDataSourceLocatorPtr dlPrompt = NULL;
      	_ConnectionPtr conn = NULL;
      	hr = dlPrompt.CreateInstance(__uuidof(DataLinks));
      	conn = dlPrompt->PromptNew();
      	if ( NULL != conn )
      	{
      		printf( "Connect: %s\n", (char*) conn->ConnectionString );
      	}
      
   	return;
   }
   
   					

3. On the Debug menu, click Start without Debugging to run the project.
4. Type the appropriate information in the Data Link Properties dialog box, and make sure that you click to select the Allow Saving Password check box.
5. Click Test Connection.
6. Click OK. If the connection test succeeded in the data link, a connection to the database is established, and a message box is displayed.

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Create an OLE DB Connection

When you create an OLE DB connection with the OLE DB managed provider in .NET, you cannot create connections to ODBC datasources. Because ODBC has its own Managed provider in .NET, you receive an error if you use the Microsoft OLE DB provider for ODBC drivers option in the Data Link Properties dialog box. Additionally, you must load ADO into the application because the data link creates an ADODB Connection object that is not compatible with the OLEDBConnection object. Therefore, you must create an ADODB Connection and assign its ConnectionString property to the ConnectionString property of the OLEDBConnection object for this to work correctly.

1. 1. Start Microsoft Visual Studio .NET, and create a new Managed C++ Application project. Name it OledbDL.cpp.
2. Replace the default code in OledbDL.cpp with the following code:

   #using <mscorlib.dll>
   #using <System.dll>
   #using <System.Data.dll>
   
   #undef EOF
   #import "c:\program files\common files\system\ole db\oledb32.dll" rename_namespace("dlinks")
   #import "c:\program files\common files\system\ado\msado15.dll" rename_namespace("ado")
   
   void TestConnection(void);
   
   #ifdef _UNICODE
   int wmain(void)
   #else
   int main(void)
   #endif
   {
       TestConnection();
       return 0;
   }
   
   void TestConnection(void)
   {
   	using namespace dlinks;
   	using namespace ado;
   	using namespace System;	
            using namespace System::Data::OleDb;
   	
   	HRESULT hr;
      	::CoInitialize( NULL );
      	IDataSourceLocatorPtr dlPrompt = NULL;
      	OleDbConnection *oleConn = new OleDbConnection();
   	_ConnectionPtr adoConn = NULL;
      	hr = dlPrompt.CreateInstance(__uuidof(DataLinks));
      	adoConn = dlPrompt->PromptNew();
   	System::String *str = (char*) adoConn->ConnectionString; // define a garbage collected string
   	oleConn->ConnectionString = str;
   
   	try
   	{
   	    oleConn->Open();
   	    if ( NULL != oleConn )
      	    {
   		Console::WriteLine("Connect: {0}\n",  oleConn->ConnectionString );
   	    }
   	}
   	catch(Exception *ex)
   	{
   		Console::WriteLine(ex->Message);
   	}
   	__finally
   	{
   		oleConn->Close();
   	}
   	return;
   }
   					

3. On the Debug menu, click Start without Debugging to run the project.
4. Type the appropriate information in the Data Link Properties dialog box, and make sure that you click to select the Allow Saving Password check box.
5. Click Test Connection.
6. Click OK. If the connection test succeeded in the data link, a connection to the database is established, and a message box is displayed.

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Additional Information

It requires additional effort to use this method to create an ODBC connection because the data link creates a connection string that is specific to OLE DB and is not compatible with the ODBC managed provider. For this to work, you must parse the ADODB connection string for the relevant information such as the user ID, password, and data source. After you obtain this information, you can use it to create a connection string that is specific to ODBC. Keep in mind that the data link only uses ODBC data source names (DSNs); therefore, you cannot create a DSN-less connection through the data link.

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