How To Access an Oracle Database Using RDO

MORE INFORMATION

The example in this article is a simple Visual Basic project that creates a DSN-Less connection against an Oracle database and executes a stored procedure. When working with Oracle and the Microsoft ODBC Driver for Oracle, there are some settings that are different than working with Microsoft SQL Server. These differences occur because you are using a different ODBC driver.

The Visual Basic 5.0 and higher Enterprise edition includes RDO 2.0 and the Microsoft ODBC Driver for Oracle. Both of these need to be installed in order to run the example project in this article.

NOTE: The ODBC driver from Oracle does not support the entire RDO 2.0 feature set (including the calling of stored procedures and binding return values).

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. But, 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 (rdooracle) and a stored procedure (rdoinsert). Following are the data definition language (DDL) scripts to create these objects:

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

        CREATE TABLE rdooracle (
                  item_number    NUMBER(3) PRIMARY KEY,
                  depot_number   NUMBER(3));
  					

• RDOINSERT: 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:

        CREATE OR REPLACE PROCEDURE rdoinsert
           (insnum IN NUMBER, outnum OUT NUMBER)
        IS
        BEGIN
        INSERT INTO rdooracle
           (Item_Number, Depot_Number)
        VALUES
           (insnum, 16);
        outnum := insnum/2;
        END;
  					

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

The above scripts can be run from SQL*Plus or from within the Visual Database Tools Add-In in the Visual Basic 5.0 Enterprise edition. Once these objects have been created, you can create the Visual Basic project that will use them.

Step-by-Step Example

This example project uses a simple form to send a bind parameter to the RDOINSERT 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 5.0 Enterprise edition. Form1 is created by default.
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, select the Options item. Click the Default Full Module View option and then click OK. This will allow you to view all of the code for this project.
4. Paste the following code into your code window:

         Option Explicit
         Dim Cn As rdoConnection
         Dim En As rdoEnvironment
         Dim CPw As rdoQuery
         Dim Rs As rdoResultset
         Dim Conn As String
         Dim QSQL As String
         Dim Response As String
         Dim Prompt As String
   
         Private Sub cmdCheck_Click()
   
             QSQL = "Select Item_Number, Depot_Number From rdooracle Where " _
             & "item_number =" & txtInput.Text
             Set Rs = Cn.OpenResultset(QSQL, rdOpenStatic, , rdExecDirect)
   
             Prompt = "Item_Number = " & Rs(0) & ".  Depot_Number = " _
             & Rs(1) & "."
   
             Response = MsgBox(Prompt, , "Query Results")
   
             Rs.Close
   
         End Sub
   
         Private Sub cmdSend_Click()
   
             CPw(0) = Val(txtInput.Text)
             CPw.Execute
   
             Prompt = "Return value from stored procedure is " & CPw(1) & "."
             Response = MsgBox(Prompt, , "Stored Procedure Result")
   
         End Sub
   
         Private Sub Form_Load()
   
             Conn = "UID=;PWD=;driver={Microsoft ODBC Driver for Oracle};" _
                  & "CONNECTSTRING=MyOracle;"
   
             Set En = rdoEnvironments(0)
             Set Cn = En.OpenConnection("", rdDriverPrompt, False, Conn)
             QSQL = "{call rdoinsert(?,?)}"
             Set CPw = Cn.CreateQuery("", QSQL)
   
         End Sub
   
         Private Sub Form_Unload(Cancel As Integer)
   
             En.Close
   
         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, RDOINSERT, 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.

Following 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. It also contains the code that creates the query that calls the stored procedure:

    Private Sub Form_Load()

       Conn = "UID=;PWD=;driver={Microsoft ODBC Driver for Oracle};" _
            & "CONNECTSTRING=MyOracle;"

       Set En = rdoEnvironments(0)
       Set Cn = En.OpenConnection("", rdDriverPrompt, False, Conn)
       QSQL = "{call rdoinsert(?,?)}"
       Set CPw = Cn.CreateQuery("", QSQL)

   End Sub
				

Note that you are not using the rdPreparedStatement object. This object has been replaced by the rdoQuery object. This is new for RDO 2.0. Also, with RDO 2.0, you do not need to explicitly create a connection object as is done in this project. You can create a stand-alone query object that is not specifically associated with a connection. To learn more about this functionality, look up the rdoQuery Object in the Visual Basic 5.0 Enterprise edition Help file.

The connect string used to open a connection to an Oracle database (or any database) is very dependent upon the underlying ODBC driver. Even though similar parameters are used by most ODBC drivers (UID, PWD, etc.), the connect string used here will work only with the Microsoft ODBC Driver for Oracle:

Conn = "UID=;PWD=;driver={Microsoft ODBC Driver for Oracle};" _
            & "CONNECTSTRING=MyOracle;"
				

The most important part of this connect string is the "CONNECTSTRING" keyword. It is used only by the Microsoft ODBC Driver for Oracle. For Microsoft SQL Server 6.5, you use the keyword "SERVER." The string assigned to CONNECTSTRING is the Database Alias that you set up in SQL*Net. This is the only difference in the connect string when connecting to an Oracle database. All of the other parameters operate as described in the Help file (under rdoConnection Object) for Visual Basic 5.0 Enterprise edition. As stated in the Help file, for a connection, you do not specify a DSN in the connect string.

Also in the Form_Load event is the code that creates the query object that calls the stored procedure:

   QSQL = "{call rdoinsert(?,?)}"
   Set CPw = Cn.CreateQuery("", QSQL)
				

With Oracle, you cannot specify a return value for a stored procedure call as you can with Microsoft SQL Server 6.5; you must use stored procedures that have output parameters as noted earlier in this article. The parameter placeholders in the QSQL string are denoted by a "?" and referenced in the order they in which they appear in the string. For more information on the use of parameter placeholders in the rdoQuery object, refer to the rdoParameter object in the Visual Basic 5.0 Enterprise edition Help file.

The remainder of the project is fairly straight-forward and well-documented in both the online Help file and Books Online, both of which come with Visual Basic 5.0. The RDO issues 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, and your Oracle 7 server documentation.