FIX: TABLEUPDATE() Fails in Remote View With Empty Memo Field

ID: Q191522

The information in this article applies to:

Microsoft ODBC Driver for Visual FoxPro, versions 3.0, 5.0

SYMPTOMS

You have a remote view to a Visual FoxPro table using the Visual FoxPro ODBC driver. When you attempt to issue a TABLEUPDATE() after replacing a memo field value with an empty string (""), the TABLEUPDATE() fails with the following error:

Connectivity error: [Microsoft][ODBC Visual FoxPro Driver]Invalid string or buffer length.

NOTE: This may also happen connecting through the Visual FoxPro ODBC driver from other clients such as MSQuery.

RESOLUTION

As a workaround, you can set the field to accept NULL values and replace the field value with NULL rather than "".

STATUS

Microsoft has confirmed this to be a bug in the Microsoft products listed at the beginning of this article. This bug has been corrected in Visual FoxPro 6.0.

MORE INFORMATION

Steps to Reproduce Behavior

Run the following code from a program (.PRG) file. It programmatically creates an ODBC User DSN called "VFP TestDB" to connect to a database container called TestDB.dbc. The .dbc is created, a table called TESTTAB is created, and a remote view (called TESTTAB_REMOTE) to that table is created. The view is USEd, the Notes memo field is replaced with the value "", and the TABLEUPDATE() is issued. TABLEUPDATE() returns .F. and the error generated is:

Connectivity error: [Microsoft][ODBC Visual FoxPro Driver]Invalid string or buffer length.

      LOCAL lcDir, lcSettings, laErrorArray[1]
      CLEAR
      SET EXCLUSIVE OFF
      CLOSE DATABASE ALL

      * Declare API function to create ODBC User DSN.
      DECLARE INTEGER SQLConfigDataSource IN odbccp32.DLL ;
         INTEGER, INTEGER, STRING, STRING
      lcDir = SET('DEFAULT')+CURDIR()
      lcSettings="DSN=VFP TestDB"+CHR(0)+;
         "Description=VFP TestDB"+CHR(0)+;
         "SourceDB="+lcDir+"testdb.dbc"+CHR(0)+;
         "SourceType=DBC"

      * Call API function to create ODBC User DSN.
      =SQLConfigDataSource(0,1,"Microsoft Visual FoxPro Driver",lcSettings)

      SET SAFETY OFF
      * Make the database.
      CREATE DATABASE 'TESTDB.DBC'

      * Make the table and index.
      CREATE TABLE 'TESTTAB.DBF' NAME 'TESTTAB' (PK C(5) NOT NULL, ;
         NOTES M NOT NULL)

      ALTER TABLE 'TESTTAB' ADD PRIMARY KEY PK TAG PK

      CLOSE DATABASE ALL
      OPEN DATABASE testdb SHARED

      * Make the remote view.
      CREATE SQL VIEW "TESTTAB_REMOTE" ;
         REMOTE CONNECT "VFP TestDB" ;
         AS SELECT * FROM TESTTAB Testtab

      * Set the view properties.
      DBSETPROP('TESTTAB_REMOTE', 'View', 'UpdateType', 1)
      DBSETPROP('TESTTAB_REMOTE', 'View', 'WhereType', 1)
      DBSETPROP('TESTTAB_REMOTE', 'View', 'FetchMemo', .T.)
      DBSETPROP('TESTTAB_REMOTE', 'View', 'SendUpdates', .T.)
      DBSETPROP('TESTTAB_REMOTE', 'View', 'UseMemoSize', 255)
      DBSETPROP('TESTTAB_REMOTE', 'View', 'FetchSize', 100)
      DBSETPROP('TESTTAB_REMOTE', 'View', 'MaxRecords', -1)
      DBSETPROP('TESTTAB_REMOTE', 'View', 'Tables', 'TESTTAB')
      DBSETPROP('TESTTAB_REMOTE', 'View', 'Prepared', .F.)
      DBSETPROP('TESTTAB_REMOTE', 'View', 'CompareMemo', .T.)
      DBSETPROP('TESTTAB_REMOTE', 'View', 'FetchAsNeeded', .F.)
      DBSETPROP('TESTTAB_REMOTE', 'View', 'FetchSize', 100)
      DBSETPROP('TESTTAB_REMOTE', 'View', 'Comment', "")
      DBSETPROP('TESTTAB_REMOTE', 'View', 'BatchUpdateCount', 1)
      DBSETPROP('TESTTAB_REMOTE', 'View', 'ShareConnection', .F.)
      * Set the view field properties.
      DBSETPROP('TESTTAB_REMOTE.pk', 'Field', 'KeyField', .T.)
      DBSETPROP('TESTTAB_REMOTE.pk', 'Field', 'Updatable', .T.)
      DBSETPROP('TESTTAB_REMOTE.pk', 'Field', 'UpdateName', 'TESTTAB.pk')
      DBSETPROP('TESTTAB_REMOTE.pk', 'Field', 'DataType', "C(5)")
      DBSETPROP('TESTTAB_REMOTE.notes', 'Field', 'KeyField', .F.)
      DBSETPROP('TESTTAB_REMOTE.notes', 'Field', 'Updatable', .T.)
      DBSETPROP('TESTTAB_REMOTE.notes', 'Field', 'UpdateName', ;
         'TESTTAB.notes')
      DBSETPROP('TESTTAB_REMOTE.notes', 'Field', 'DataType', "M")

      SET SAFETY ON

      * Add a couple of records to the table.
      INSERT INTO TESTTAB VALUES ("A", "1234567890")
      INSERT INTO TESTTAB VALUES ("B", "1234567890")
      CLOSE DATABASE ALL
      OPEN DATABASE testdb

      * Open the view.
      USE testdb!TESTTAB_remote

      *Replace field with "" and issue TABLEUPDATE()
      REPLACE NOTES WITH ""
      IF !TABLEUPDATE(.T.)
         ?"Tableupdate failed with the following error:"
         =AERROR(laErrorArray)
         ?laErrorArray(2)
         =TABLEREVERT()
      ENDIF

TABLEUPDATE() returns .F. indicating that it failed. The error returned from AERROR() is:

Connectivity error: [Microsoft][ODBC Visual FoxPro Driver]Invalid string or buffer length.

If the memo field is set to accept nulls and the REPLACE replaces the value with NULL, the error does not occur. You can do the following within Visual FoxPro:

You can demonstrate this by changing the preceding CREATE TABLE line to read:

CREATE TABLE 'TESTTAB.DBF' NAME 'TESTTAB' (PK C(5) NOT NULL, ; NOTES M NULL)

-and- change the REPLACE line to read:

REPLACE NOTES WITH NULL

To employ this workaround from within a Visual FoxPro form, for instance, make the following changes:

Set the following environment setting in Visual FoxPro 5.0. This makes the NULL display as an empty string.
```
      SET NULLDISPLAY TO "" 
```

In an Editbox Valid method, you could add the following code to ensure that the NULL is used if the Value property of the Editbox is empty:
```
      IF EMPTY(This.Value)
         This.Value = NULL
      ENDIF 
```

REFERENCES

Additional query words: kbVFp300bbug kbVFp500abug kbVFp600bug kbODBC

Keywords :
Version : WINDOWS:3.0,5.0
Platform : WINDOWS
Issue type : kbbug