HOWTO: Implement Optional Parameter with UserConnection Designer

• Microsoft Visual Basic Enterprise Edition for Windows, version 5.0

SUMMARY

Due to a limitation of ODBC, the UserConnection Designer cannot directly implement a query based on stored procedures with optional parameters. This article discusses two alternatives to work around this limitation.

The first alternative is to create two (or more) query objects based on user-defined SQL. Both query objects use ODBC call syntax to invoke the same stored procedure; one using a parameter, the other without. Depending on the situation, the client code can decide which query to use.

The second option is to add a public method to the UserConnection object. This method will decide the ODBC call syntax dynamically, with or without parameters, and return the correct results.

MORE INFORMATION

The following sample uses SQL Server and the Pubs sample database. This sample uses a ListBox and two CommandButtons to demonstrate the two approaches described above. The ListBox is loaded with values from the au_id column of the authors table. When an item from the list is selected, it is then passed to the stored procedure and the record count reflecting the single record is returned. If no list item is selected, no parameter is passed to the stored procedure and the total record count is again returned.

Task One: Create the Example Stored Procedure

1. This SQL Server stored procedure accepts an optional input parameter as au_id and returns a resultset of the count of total selected records.

2. To create this stored procedure, place the following CREATE PROCEDURE T-SQL in the SQL window of ISQL/W and execute it:

         CREATE PROCEDURE TestProc (@IDCol varchar(11) = NULL) AS
            IF @IDCol = NULL
               select count(au_id) from authors
            ELSE
               select count(au_id) from authors where au_id = @IDCol
   
   

Task Two: Create the UserConnection

1. Start a new project in Visual Basic and choose "Standard EXE." Form1 is created by default.

2. From the Project menu, select Components, select the Designer tab, and then place a check next to Microsoft UserConnection.

3. From the Project menu, select Add ActiveX Designer, and then select Microsoft UserConnection. This will bring up a dialog titled UserConnection1 Properties.

4. On the Connection tab, select either a DSN or DSN-less connection and fill in the appropriate information. If you select DSN-less, make sure you specify a database in the Other ODBC Attributes area with database=Pubs. On the Authentication tab, fill in your username and password, and place a check next to Save Connection Information for Design Time. On the Miscellaneous tab, in the Other section, choose Use ODBC cursor library because you have more than one Select statement in the stored procedure.

5. Click OK to save this information and return to the Designer window.

6. Insert a new Query by right-clicking on UserConnection1 and choosing Insert Query or by clicking on the Insert Query toolbar icon. Change the name of the Query from Query1 to TestProc1.

7. From the Source of Query, choose Based on User-Defined SQL. Then type the following SQL into the TextBox:

         {call TestProc (?)}
   

8. Click OK to save this information.

9. Repeat Step 6 through 8 to add another new query. Name this query as TestProc2. Type the following SQL into the TextBox of User-Defined SQL:

         {call TestProc ()}
   

Task Three: Build the Visual Basic Code

1. Add two CommandButtons, Command1 and Command2, to Form1.

2. Add a ListBox control, List1, to Form1.

3. Paste the following code in the General Declaration section of Form1:

         Dim cn As New UserConnection1
   

         Private Sub Command1_Click()
            Dim rs As rdoResultset
   
            If List1.ListIndex = -1 Then
               cn.TestProc2
            Else
               cn.TestProc1 (List1.Text)
            End If
            Set rs = cn.LastQueryResults
            MsgBox rs(0) & " records selected"
            rs.Close
            List1.ListIndex = -1
         End Sub
   
         Private Sub Command2_Click()
            Dim rs As rdoResultset
            If List1.ListIndex = -1 Then
               Set rs = cn.TestProc3
            Else
               Set rs = cn.TestProc3(List1.Text)
            End If
            MsgBox rs(0) & " records selected"
            rs.Close
         End Sub
   
         Private Sub Form_Load()
            List1.AddItem "648-92-1872"
            List1.AddItem "722-51-5454"
            List1.AddItem "756-30-7391"
   
            Command1.Caption = "Alternative 1"
            Command2.Caption = "Alternative 2"
   
            cn.EstablishConnection
         End Sub
   
   

4. Paste the following code under UserConnection object: (Hint: Select View Code from the UserConnection toolbar.)

         Public Function TestProc3(Optional theID As Variant) As rdoResultset
            Dim sCallSyntax As String
            If IsMissing(theID) Then
               sCallSyntax = "{call TestProc()}"
            Else
               sCallSyntax = "{call TestProc('" & theID & "')}"
            End If
            Set TestProc3 = Me.OpenResultSet(sCallSyntax)
         End Function
   
   

5. Start the program or press the F5 key.

REFERENCES

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

   ARTICLE-ID: Q166281
   TITLE     : HOWTO: Create and Implement a UserConnection