PRB: Database Errors Not Shown When Closing Form

ID: Q141172

The information in this article applies to:

Microsoft Visual Basic Standard, Professional, and Enterprise Editions, 16-bit and 32-bit, for Windows, version 4.0

SYMPTOMS

When a form with one or more data controls on it is closed, all changed information in bound data controls is, by default, written to the database before the database is closed. However, any errors that result from this default update are not displayed. For example, if a field has its Required property set to True, and a form that contains an empty text box bound to that field is closed, no error will be shown.

RESOLUTION

Placing a call to the data control's UpdateRecord method in the form's Unload event causes all errors to be shown and also makes it possible to trap for these errors and act accordingly.

STATUS

This behavior is by design.

MORE INFORMATION

Steps to Reproduce

Start Visual Basic, or if it is already running, click New Project on the File menu.

Double click the data control button in the Toolbox to add a new data control, named Data1, to the form.

Set the following properties of Data1:
```
       DatabaseName: <path to your VB directory>\biblio.mdb 
```
Leave the RecordSource property blank for now.

Click and drag two text boxes onto the form.

Set the DataSource property of both text boxes to Data1; also set the DataField property of Text1 to "Au_ID" and the DataField property of Text2 to Author.

Click and drag a command button, named Command1 by default, onto the form.

Add the following code to the Command1_Click procedure. This tells Jet that the Au_ID field must have a non-null value before it is committed to the database.
```
       Private Sub Command1_Click()
       Data1.Database.TableDefs("Authors").Fields("Au_ID").Required = True
       Data1.RecordSource = "Authors"
       Data1.Refresh
    End Sub 
```
The line setting the Required property can't be placed in the Form_Load event because the connection to the database is not guaranteed to be valid until the Form_Load event is finished.

On the Run menu, click Start (ALT, R, S) or press F5 to start the application.

Press the Command1 button to set the Required property of the Au_ID field to True.

Select and delete the 1 in the Au_ID field of the first record. Now double-click the control box in the upper-left corner of the form to close the form. The database will be closed and no error will be raised.

If you changed the current record or did an update after deleting the value in the Au_ID field, Visual Basic would have returned a "Data type conversion error." Open the database again and examine the Au_ID field of the first record; the 1 was never deleted (although this behavior is not guaranteed). Add the "Data1.UpdateRecord" line to the Form1_Unload event to allow the error to be shown and/or trapped.

The Biblio.mdb database is used in many examples and should not be permanently changed. After experimenting with this problem, remember to change the Required value of the Au_ID field back to its original value of False. This can be done by rerunning the above program and clicking the command button after changing the code in the Command1_Click procedure to:


   Private Sub Command1_Click()
   Data1.Database.TableDefs("Authors").Fields("Au_ID").Required = False
   End Sub

Additional query words: 4.00 vb4win vb4all

Keywords : kbDatabase
Version : WINDOWS:4.0
Platform : WINDOWS
Issue type :