INFO: Visual Basic Accessing an Oracle Database Using ADO

With Visual Basic and ADO, you have the ability to connect to an Oracle database through a DSN-Less connection, execute a stored procedure using parameters, and get return values from that stored procedure. The example in this article illustrates all of this functionality.

To run the sample code in this article, you may need to download and install the Microsoft Data Access Components if you are using Visual Basic 5.0. The MDAC Components are located at: http://msdn.microsoft.com/en-us/data/aa937729.aspx (http://msdn.microsoft.com/en-us/data/aa937729.aspx) The following example was created against an Oracle 7.3 database through a SQL*Net 2.3 connection. All of the following code (including the stored procedure) should work fine with Oracle 7.2. However, the Microsoft ODBC Driver for Oracle Help file states that it only supports SQL*Net 2.3.

There are two objects that need to be created on the Oracle database; a table (adooracle) and a stored procedure (adoinsert).

NOTE: If you have worked through the following Microsoft Knowledge Base article then you can use the Oracle objects created in that article (rdooracle and rdoinsert). Just change the Visual Basic code below accordingly:

Here are the data definition language (DDL) scripts to create these objects:

ADOORACLE - This is just a two-column table with the first column set as the primary key:



ADOINSERT - This procedure accepts a single numeric input parameter and returns a single numeric output parameter. The input parameter is first used by an input statement, then it is divided by 2 and set as the output parameter:


In SQL 3.3, use a foward slash (/) to terminate and execute the script declaring the stored procedure.

NOTE: You must use Procedures that have output parameters and not Functions when working with Oracle and ADO parameters.

The preceding scripts can be run from SQL*Plus. Once these objects have been created, you can create the Visual Basic project that will use them.

This sample project uses a simple form to send a bind parameter to the ADOINSERT stored procedure and then return the output parameter from that procedure. Here are the steps to create the project:

1. Open a new project in Visual Basic and add a Reference to the Microsoft ActiveX Data Objects library.
2. Place the following controls on the form:

   
      Control      Name      Text/Caption
   
      Button      cmdCheck    Check
      Button      cmdSend     Send
      Text Box    txtInput
      Label       lblInput    Input:
   
   						

3. From the Tools menu, choose Options, Click the "Default Full Module View" option, and then click OK. This allows you to view all of the code for this project.
4. Paste the following code into your code window:

   
       Option Explicit
       Dim Cn As ADODB.Connection
       Dim CPw1 As ADODB.Command
       Dim CPw2 As ADODB.Command
       Dim Rs As ADODB.Recordset
       Dim Conn As String
       Dim QSQL As String
   
       Private Sub cmdCheck_Click()
   
         CPw1(0) = Val(txtInput.Text)
   
         Set Rs = CPw1.Execute
   
         MsgBox "Item_Number = " & Rs(0) & ".  Depot_Number = " & Rs(1) & "."
   
         Rs.Close
   
       End Sub
   
       Private Sub cmdSend_Click()
   
          CPw2(0) = Val(txtInput.Text)
   
          CPw2.Execute
   
          MsgBox "Return value from stored procedure is " & CPw2(1) & "."
   
       End Sub
   
       Private Sub Form_Load()
   
          'You will need to replace the "*" with the appropriate values.
          Conn = "UID=*****;PWD=****;DRIVER={Microsoft ODBC for Oracle};" _
               & "SERVER=*****;"
   
          Set Cn = New ADODB.Connection
   
          With Cn
            .ConnectionString = Conn
            .CursorLocation = adUseClient
            .Open
          End With
   
          QSQL = "Select Item_Number, Depot_Number From adooracle Where " _
          & "item_number = ?"
   
          Set CPw1 = New ADODB.Command
   
          With CPw1
            .ActiveConnection = Cn
            .CommandText = QSQL
            .CommandType = adCmdText
            .Parameters.Append .CreateParameter(, adInteger, adParamInput)
          End With
   
          QSQL = "adoinsert"
   
          Set CPw2 = New ADODB.Command
   
          With CPw2
            .ActiveConnection = Cn
            .CommandText = QSQL
            .CommandType = adCmdStoredProc
            .Parameters.Append .CreateParameter(, adInteger, adParamInput)
            .Parameters.Append .CreateParameter(, adDouble, adParamOutput)
          End With
   
       End Sub
   
       Private Sub Form_Unload(Cancel As Integer)
   
          Cn.Close
          Set Cn = Nothing
          Set CPw1 = Nothing
          Set CPw2 = Nothing
   
       End Sub
   
   					

5. Run the project.

When you enter a number in the text box, txtInput, and click the Send button, the Oracle stored procedure, ADOINSERT, is called. The number you entered in the text box is used as the input parameter for the procedure. The output parameter is used in a message box that is called after the stored procedure has completed processing. With your original value still in the text box, click the "Check" button. This creates a simple read-only resultset that is displayed in another message box.

What follows is a detailed explanation of the code used in this demonstration project.

The Form_Load event contains the code that creates the DSN-Less connection: Once you create the ADO connection object (Cn), you set several of its parameters using the WITH statement.

The connect string that is used to open a connection to an Oracle database (or any database for that matter) is very dependant on the underlying ODBC driver. You can see in the connect string below that the Microsoft Oracle driver you are using is named specifically by DRIVER=: The most important part of this connect string is the "SERVER" keyword. The string assigned to SERVER is the Database Alias which you set up in SQL*Net. This is the only difference in the connect string when connecting to an Oracle database. For a DSN-Less connection, as is stated in the Help file, you do not specify a DSN in the connect string.

Also in the Form_Load event is the code that creates the two ADO Command objects used in the project: The first Command object (CPw1) is a simple parameterized query. The CommandText has one parameter that is the item_number for the where clause. Note that the CommandType is set to adCmdText. This is different than the adCmdStoredProc CommandType in the second Command object (CPw2). The following is from the ADO Help HTML file: Using the WITH command, you can create and append parameters to the command object easily. The first parameter of the CreateParameter function is for the name of the parameter. This has been left blank because the sample program uses the index of the parameters collection to identify the individual parameters (such as CPw1(0) to identify the first parameter). The sample program uses adInteger and adDouble datatypes. If it had used a variable length datatype, then the size parameter of the CreateParameter function would need to be set. Again, from the ADO Help HTML: The remainder of the project is fairly straightforward and well-documented in both the Online Help file and Books Online which come with Visual Basic. The ADO issues that are critical to working with Oracle (the connect string and the calling of stored procedures) have been detailed in this project.

For more information on these issues, please consult your Oracle SQL*Net 2.3 documentation, the Help file for the Microsoft ODBC Driver for Oracle, the ADO HTML that comes with MDAC, Books Online that comes with Visual Basic 6.0 or your Oracle 7 server documentation.

Microsoft ODBC Driver for Oracle Help File

ADO Help HTML

"Oracle PL/SQL Programming" by Steven Feuerstein

"Hitchhiker's Guide to Visual Basic & SQL Server" by William Vaughn, Fifth Edition

For additional information, please see the following articles in the Microsoft Knowledge Base: