PRB: CLEAR ALL Removes Back-Links from Data Environment Object (142394)


The information in this article applies to:

  • Microsoft Visual FoxPro for Windows 3.0
  • Microsoft Visual FoxPro for Windows 3.0b
This article was previously published under Q142394

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
Modification Type:MajorLast Reviewed:9/30/2003
Keywords:KB142394
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