Q142394: PRB: CLEAR ALL Removes Back-Links from Data Environment Object

Article: Q142394
Product(s): Microsoft FoxPro
Version(s): WINDOWS:3.0,3.0b
Operating System(s): 
Keyword(s): 
Last Modified: 10-FEB-2000

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The information in this article applies to:

- Microsoft Visual FoxPro for Windows, versions 3.0, 3.0b 
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SYMPTOMS
========

If the CLEAR ALL command is issued with an open Data Environment Object, the
back-links of the tables contained in the Data Environment are destroyed.
Consecutive access of these tables will yield this error:

  Table 'tablename.dbf' is not marked as belonging to the 'databasename'
  database. Would you like to create the back link to mark it?

RESOLUTION
==========

The tables must be opened exclusively to properly update the back links. If the
tables are not opened exclusively the following error will occur in the Init
event of the DataEnvironment class:

  File must be opened exclusively.

To work around this behavior, be sure to release all DataEnvironment objects
before issuing the CLEAR ALL command.

STATUS
======

This behavior is by design.

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

Data Environments can be classed programatically. Once instantiated, you may
issue the CLEAR ALL command with open tables and database containers. If the
CLEAR ALL command is issued with an open Data Environment Object, the tables
open at that time lose their links to the database container.

This does not occur with forms' Data Environments.

Code to Demonstrate Behavior
----------------------------

The following program demonstrates this behavior. Each time this program is run
subsequent to the first time, Visual FoxPro produces the error listed above for
each table that the DataEnvironment class defines.

  SET DEFAULT TO c:\vfp
  CLOSE DATA
  oDe = CreateObject('de')
  CLEAR ALL    && remove this line, and run the program twice to
               && resolve the problem

  DEFINE CLASS de AS DataEnvironment

  Name = "DE"
  AutoCloseTables = .F.
  AutoOpenTables = .T.
  InitialSelectedAlias = "customer"

  ADD OBJECT oCustomer AS cursor WITH ;
     Alias = 'customer', ;
     Database = CURDIR() + 'samples\data\testdata.dbc', ;
     CursorSource = 'customer', ;
     Exclusive = .T.

  PROCEDURE Init
     THIS.OpenTables
  ENDPROC
  ENDDEFINE

Additional query words: VFoxWin

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Keywords          :  
Technology        : kbVFPsearch kbAudDeveloper kbVFP300 kbVFP300b
Version           : WINDOWS:3.0,3.0b

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