PRB: ON ERROR Not Called When Trigger Fails in Browse or Grid

ID: Q130131

3.00 WINDOWS

  kbprb kbdocerr

The information in this article applies to:

Microsoft Visual FoxPro for Windows, version 3.0

SYMPTOMS

Triggers that fail while working interactively in a Browse or a Grid are not captured by the ON ERROR Routine. Instead the Default Message, "Trigger Failed" is displayed. This seems inconsistent with what is documented in the Help file and in the "Language Reference" manual under CREATE TRIGGER.

CAUSE

This is because the firing of a trigger in the context of a Browse or Grid leaves the control in the hands of the Browse or Grid after the trigger fires. If the normal error handler (the one that allows for ON ERROR) is called, the option of RETRY becomes applicable. But because the Trigger code finished executing, the last command to be retried is the Browse.

Therefore, choosing the RETRY option results in two problems:

The Browse is retried instead of the trigger.
A new Browse or Grid is instantiated.

This scenario could result in an infinite loop.

WORKAROUND

One way to work around this problem is to trap the failed triggers at the Engine level, not at the Object level. In this case, put the appropriate code to handle erroneous conditions in the trigger itself. This workaround is shown below in the "More Information" section.

STATUS

This behavior is by design. We are researching this design decision and will post new information here in the Microsoft Knowledge Base if it becomes available.

MORE INFORMATION

Steps to Reproduce Behavior

1. Execute the following code to create a DBC that contains a table with a

   delete trigger and to set up an ON ERROR routine:

   CLOSE ALL
   CREATE DATABASE dbTEST
   CREATE TABLE Test1 (Fld N(3), Fld2 C(3))
   CREATE TRIGGER ON Test1 FOR DELETE AS .F.
   ON ERROR WAIT WINDOW 'Delete Trigger Failed'

2. Open the dbTEST database, then open the table Test1 with the USE

   command, and use the BROWSE command to browse the table. Then issue the
   following two commands from the Command window:

   APPEND BLANK
   DELETE NEXT 1

   When the Trigger fails, the Wait window is displayed. Everything is as
   expected.

3. Browse the table again, and use the mouse to delete a record. This time

   when the Trigger fails, no Wait window is displayed. Instead the
   default system message "Trigger Failed" is displayed.

Steps to Implement Workaround

1. Change the CREATE TRIGGER statement to read:

   CREATE TRIGGER ON Test1 FOR DELETE AS MyDelTrig()

2. Remove the ON ERROR WAIT WINDOW 'Delete Trigger Failed' line from the '

   code.

3. Add the following Procedure to the "Stored Procedures":

   PROCEDURE MyDelTrig
   IF Fld >= 10
      RETURN .T.
   ELSE
      =MESSAGEBOX("Test1 must be greater than '10' to be deleted ;
      "+CHR(13)+"Record Number: "+STR(RECNO())+" Was NOT deleted!")
         IF CURSORGETPROP('BUFFERING') > 1
            =TABLEREVERT(.F.) &&Buffering enabled Revert record.
         ELSE
            RECALL NEXT 1 &&Buffering NOT enabled Revert record.
         ENDIF
   ENDIF

Additional reference words: 3.00 VFoxWin

KBCategory:   kbprb kbdocerr

KBSubcategory: FxprgBrowse

Keywords          : kbcode FxprgBrowse 
Version           : 3.00
Platform          : WINDOWS