FIX: Delete Trigger Fires Out of Order

The information in this article applies to:

• Microsoft Visual FoxPro for Windows, version 3.0

SYMPTOMS

The Delete trigger fires immediately when buffering level is 2-Record (Pessimistic) or 3-Record (Optimistic).

CAUSE

With these buffering levels, the Delete trigger should fire when you leave a record. However, it fires immediately as though the buffering level was 1 (Off - No Buffering).

STATUS

Microsoft has confirmed this to be a problem in the Microsoft products listed at the beginning of this article. This problem was corrected in Visual FoxPro 3.0b for Windows.

MORE INFORMATION

Rules and triggers are there to protect the integrity of the data. The order in which the rules and triggers fire depends directly on the buffering in effect at that time. With Buffering levels 2 or 3, the Delete trigger should not fire until you attempt to leave the record instead of immediately because that record is buffered until you move the record pointer off that record.

Steps to Set Up Example to Reproduce Problem

1. To duplicate the behavior of the firing order of rules and triggers, create the following sample database and table with the specified stored procedures. Enter the following in the Command window:

      CREATE DATABASE Mydata      && Creates the database container
      MODIFY DATABASE Mydata      && Opens the database container
   
   

2. Enter the following procedures into the Stored Procedures:

   PROCEDURE MYDEL =MESSAGEBOX("My Delete Trigger")

3. Enter the following in the Command window:

   CREATE TABLE Mytab(Fname C(15),Lname C(15)) CREATE TRIGGER ON Mytab FOR DELETE AS Mydel()

Steps to Reproduce Problem

1. In the Command window, type:

   OPEN DATABASE Mydata

      SET MULTILOCKS ON         && Required for buffering.
      =CURSORSETPROP("Buffering",1)   && Turns Buffering Off
   
      Or on the Tools menu, click Options. In the Data tab, set Buffering to
      Off
   
   

2. To verify the setting, enter the following on a new line in the Command window:

   ? CURSORGETPROP("Buffering")

   This will return the value of the Buffering level: 1=Off, 2=Record(Pessimistic), 3=Record(Optimistic), 4=Table(Pessimistic), and 5=Table(Optimistic).

3. Select the title bar of the table, click the secondary (right) mouse button, and choose Browse.

4. With Table Buffering set Off, press CTRL+Y to append a blank record.

5. Mark any record for deletion. The Delete trigger fires immediately. This is correct behavior when Buffering is level 1 - Off.

6. Enter the following commands in the Command window:

         SET MULTILOCKS ON      && If you have not done so previously.
         =CURSORSETPROP("Buffering",2)
   
      Or on the Tools menu, click Options. Then in the Data tab, set Buffering
      to 2-Record (Pessimistic). If no data exists, press CTRL+Y to append a
      blank record.
   
   

7. Mark any record for deletion, the Delete trigger fires immediately. This is incorrect behavior when Buffering is level 2 or 3.

8. Change Buffering to 4 (Pessimistic Table Locks) by typing in the following Command window:

         SET MULTILOCKS ON      && If you have not done so previously.
         =CURSORSETPROP("Buffering",4)   && Table(Pessimistic)
   
      Or on the Tools menu, click Options. Then in the Data tab, set Buffering
      to 4-Table (Pessimistic). If no data exists, press CTRL+Y to append a
      blank record. Then do the following:
   
      a. If no entries exist, press CTRL+Y to append a blank record. Enter
         at least 2 records.
   
      b. Mark any record for deletion. The Delete trigger doesn't fire
         immediately. This is correct behavior. Changes to the table have been
         buffered, so they are not be written until a Tableupdate is issued.
   
      c. Type the following in the Command window:
   
         =TABLEUPDATE(.t.)
   
         Now the Delete trigger fires as the table is updated from the buffer.
         The same correct behavior occurs for buffering level 5.
   
   

9. Change the buffering level to 1 (Off) by typing in the following Command window:

         =CURSORSETPROP("Buffering",1)
   

   Or on the Tools menu, click Options. Then in the Data tab, set Buffering to 1 (Off). Then you can pack or recycle the records.