Microsoft KB Archive/176936

= INFO: Visual Basic Accessing an Oracle Database Using ADO =

Article ID: 176936

Article Last Modified on 3/2/2005

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APPLIES TO


 * Microsoft Visual Basic 5.0 Enterprise Edition
 * Microsoft Visual Basic 6.0 Enterprise Edition
 * Microsoft ActiveX Data Objects 1.5
 * Microsoft ActiveX Data Objects 2.0
 * Microsoft ActiveX Data Objects 2.1 Service Pack 2
 * Microsoft ActiveX Data Objects 2.5
 * Microsoft ActiveX Data Objects 2.6
 * Microsoft ActiveX Data Objects 2.7

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This article was previously published under Q176936





For a Microsoft Visual Basic .NET version of this article, see 308071.



SUMMARY
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.



MORE INFORMATION
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/dataaccess 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:

167225 HOWTO: Access an Oracle Database Using RDO

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:

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

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:

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

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:

 Open a new project in Visual Basic and add a Reference to the Microsoft ActiveX Data Objects library.  Place the following controls on the form:  Control     Name      Text/Caption

Button     cmdCheck    Check Button     cmdSend     Send Text Box   txtInput Label      lblInput    Input:

 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.  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

 Run the project.</li></ol>

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: Conn = "UID= ;PWD= ;DRIVER={Microsoft ODBC for Oracle};" _ & "SERVER=<MyServer>;"

Set Cn = New ADODB.Connection

With Cn      .ConnectionString = Conn .CursorLocation = adUseClient .Open End With

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=: Conn = "UID= ;PWD= ;DRIVER={Microsoft ODBC for Oracle};" _ & "SERVER==<MyServer>;"

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: 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 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:

"Use the CommandType property to optimize evaluation of the CommandText property. If the CommandType property value equals adCmdUnknown (the default value), you may experience diminished performance because ADO must make calls to the provider to determine if the CommandText property is an SQL statement, a stored procedure, or a table name. If you know what type of command you're using, setting the CommandType property instructs ADO to go directly to the relevant code. If the CommandType property does not match the type of command in the CommandText property, an error occurs when you call the Execute method."

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:

"If you specify a variable-length data type in the Type argument, you must either pass a Size argument or set the Size property of the Parameter object before appending it to the Parameters collection; otherwise, an error occurs."

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.

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