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Q299020: FIX: Index Corruption Updating Same Record from FoxPro

Article: Q299020
Product(s): Microsoft FoxPro
Version(s): 6.0
Operating System(s): 
Keyword(s): kbDatabase kbvfp kbvfp600 kbvfp600bug KbDBFDBC kbGrpDSFox kbDSupport kbvfp700fix kbvfp7
Last Modified: 29-AUG-2001

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The information in this article applies to:

- Microsoft Visual FoxPro for Windows, version 6.0 
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SYMPTOMS
========

When Buffering is set to 3 (Optimistic row) and two or more users edit a record
and commit changes, the table index may become corrupt, causing blank
("phantom") records to appear.

CAUSE
=====

Internally, FoxPro calls functions that lock a record and determine that the
record was changed by another user. The status of current value of the record is
adjusted, but the value for each index is not updated. As a result, an
inconsistency is created between the index buffer and the new record.

STATUS
======

This problem was corrected in Microsoft Visual FoxPro version 7.0 for Windows.

MORE INFORMATION
================

Steps to Reproduce Behavior
---------------------------

1. In Visual FoxPro version 6.0 (VFP6), paste the following code in a new
  program:

  ON ERROR *
  TABLEREVERT(.T.)
  ON ERROR
  CLEAR ALL
  CLEAR
  SET MULTILOCKS ON
  SET SAFETY OFF
  PUBLIC mErr
  mErr = 0

  ON ERROR mErr = ERROR()
  USE table1 EXCLUSIVE
  ON ERROR

  IF mErr  < 2
  	DO maketable
  	? "Making table."
  ELSE
  	? "Not making table."
  	? mErr
  ENDIF

  USE table1 ORDER 1 SHARED
  CURSORSETPROP("Buffering",3)
  REPLACE NAME WITH ALLTRIM(NAME) + IIF(mErr < 2,"x","y")
  IF mErr >2
  	? "TableUpdate: ",TABLEUPDATE(0,.T.)
  	CLOSE DATABASES ALL
  	RETURN
  ENDIF

  PUBLIC ox
  ox = NEWOBJECT("myform")
  ox.SHOW

  *~~~~~~~~~~~~~~~~~~~~~~~~~~~
  DEFINE CLASS myform AS FORM
  	AUTOCENTER = .T.
  	WIDTH = 350
  	HEIGHT = 300
  	MINBUTTON = .F.
  	MAXBUTTON = .F.
  	BORDERSTYLE = 2
  	CAPTION = []
  	ADD OBJECT cmdUpdate AS COMMANDBUTTON
  	ADD OBJECT grdMyGrid AS GRID
  	PROCEDURE cmdUpdate.CLICK
  		ACTIVATE SCRE
  		?"TableUpdate: ",TABLEUPDATE(0,.T.)
  	ENDPROC
  	PROCEDURE INIT
  		WITH THIS
  			.grdMyGrid.TOP = 75
  			.grdMyGrid.LEFT = 20
  			.cmdUpdate.CAPTION = "TableUpdate(0,.T.)"
  			.cmdUpdate.TOP = 10
  			.cmdUpdate.WIDTH = 120
  			.cmdUpdate.HEIGHT = 40
  			.cmdUpdate.LEFT = 100
  			IF mErr >2
  				THIS.cmdUpdate.CLICK
  			ENDIF
  		ENDWITH
  	ENDPROC
  	PROCEDURE DESTROY
  		ACTIVATE SCREEN
  		LIST
  		CLOSE DATABASES ALL
  	ENDPROC
  ENDDEFINE

  PROCEDURE maketable
  	CLOSE DATABASES ALL
  	CREATE TABLE table1 (NAME c(10))
  	INSERT INTO table1 VALUES ('John')
  	INSERT INTO table1 VALUES ('Mary')
  	INDEX ON NAME TAG NAME
  ENDPROC

2. Save the program as Repro1.prg. Then, save the program a second time as
  Repro2.prg. Be sure to save both programs to the same folder.

3. Run Repro1.prg in this instance of VFP6.

4. Open a second instance of VFP6 and run Repro2.prg.

5. Return to the first instance of VFP6 and click the command button on the form
  that is displayed. Press the DOWN ARROW key to enter the grid.

You now see a blank, "phantom" record in the grid. If the Status bar is
available, note that there are only two records in the table that the grid is
displaying, although the grid seems to contain three records.

Additional query words:

======================================================================
Keywords          : kbDatabase kbvfp kbvfp600 kbvfp600bug KbDBFDBC kbGrpDSFox kbDSupport kbvfp700fix kbvfp700 kbfixlist
Technology        : kbVFPsearch kbAudDeveloper kbVFP600
Version           : :6.0
Issue type        : kbbug
Solution Type     : kbfix

=============================================================================

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