PRB: Deleted Records are Committed with TABLEUPDATE

• Microsoft Visual FoxPro for Windows, version 3.0

SYMPTOMS

A table is opened and table buffering is enabled. During execution of a program, records are added and deleted. When the TABLEUPDATE(.T.) function is used to commit the changes, the records that were appended and then deleted are also committed to the table, and they retain their deleted status. You might expect that records appended and then deleted would not be included in the table, but this is not the case.

CAUSE

Deleting a record does not actually delete information. The delete flag is logical information that determines whether a record needs to be removed at a later date. In the same fashion, deleting a record while buffering is enabled places a flag in the record, so the record (with the delete flag) is committed when a TABLEUPDATE is issued.

RESOLUTION

If you do not want newly added and deleted records to be committed, you can scan the table and search for the appended records. If an appended record has been deleted, use the TABLEREVERT() function to discard changes. The following example illustrates this alternative. This example uses local data.

   CLOSE ALL
   CLEAR ALL
   SET MULTILOCKS ON
   SET EXCLUSIVE OFF
   **************************************************
   * CREATES A SAMPLE DATABASE AND A SAMPLE TABLE
   ***************************************************
   CREATE DATA test
   CREATE TABLE Tblbuffer (field1 I , field2 c(10))
   INSERT INTO tblbuffer  VALUES (1, 'first')
   INSERT INTO tblbuffer VALUES (2, 'second')
   INSERT INTO tblbuffer  VALUES (3, 'third')
   ****************************************************
   * Sets Optimistic Table Buffering on
   ****************************************************

   =CURSORSETPROP('buffering',5)
   ****************************************************
   * Appends two blank records and deletes one
   ****************************************************
   APPEND BLANK
   REPLACE field2 WITH 'ABC'
   APPEND BLANK
   REPLACE field2 WITH  'DEF'
   DELETE
   ******************************************************
   * Updates table. If records have an append status, check
   * for their deleted flag. If they are deleted , issue a
   * TABLEREVERT().
   *
   GO TOP
   liNextRecord=RECNO()
   DO WHILE liNextRecord!=0
   IF DELETED() AND "4" $ STR(GETFLDSTATE(0))
       =TABLEREVERT()
   ELSE
       =TABLEUPDATE()
   ENDIF
    liCurrRecno=RECNO()
    liNextRecord=GETNEXTMODIFIED(liCurrRecno)
    IF !EOF()
      SKIP
    ENDIF
    ENDDO

   ** BROWSE the table to see the problem
   BROWSE

STATUS

This behavior is by design.

REFERENCES

For more information about the GETFLDSTATE() function, search for GETFLDSTATE() in the Visual FoxPro Help file.