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Microsoft KB Archive/168837

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Article ID: 168837

Article Last Modified on 10/11/2006



APPLIES TO

  • Microsoft Visual Basic 5.0 Professional Edition
  • Microsoft Visual Basic 5.0 Enterprise Edition
  • Microsoft Visual Basic 4.0 Professional Edition
  • Microsoft Visual Basic 4.0 32-Bit Enterprise Edition
  • Microsoft Visual FoxPro 3.0 Standard Edition
  • Microsoft Visual FoxPro 5.0 Standard Edition



This article was previously published under Q168837

SYMPTOMS

Trying to set a Visual FoxPro Date field to Null via DAO/ODBC results in the following error:

"Run-time error '3162':

Null Is Invalid."

CAUSE

The FoxPro ODBC driver does not use Null for an empty date.

RESOLUTION

Set the date field to 12/30/1899 instead. The Visual FoxPro ODBC driver translates this value into an empty date.

STATUS

This behavior is by design.

MORE INFORMATION

In Visual Basic and other VBA and DAO applications, dates are stored as the number of days since 12/30/1899. This date is stored internally as the number 0. The Visual FoxPro ODBC driver takes this 0 value to represent an empty date.

Steps to Reproduce Behavior

  1. Create and execute the following Visual FoxPro program:

          CREATE DATABASE ztest
          CREATE TABLE ztest (dfield d)
          APPEND BLANK
          REPLACE dfield WITH {3/15/96}
          USE
                            
  2. In Visual FoxPro, modify the Database "ztest" and add the table "ztest" to the database. Add an additional character field and create a Primary Key (this is required for the ODBC driver to write back to the table). Exit Visual FoxPro and create a Visual FoxPro data source called ztest, which points to the database ZTEST.DBC.
  3. Create a new Visual Basic or VBA project. Make sure that Microsoft DAO 3.0 or 3.5 object library is included in your References.
  4. Add the following code to a Module:

          Sub Test_VFP_Date()
          Dim db As Database, rs As Recordset
            Set db = OpenDatabase("", False, False, _
                     "ODBC;database=testdata;uid='',pwd=;dsn=ztest")
            Set rs = db.OpenRecordset("ztest")
            rs.Edit
            rs!dfield = Null
            rs.Update
          End Sub
                            
  5. Run the code from the Immediate Window. If prompted for ODBC connection information, select the ztest data source. Then, select the ztest table and click OK.
  6. You will receive the run-time error described above for the line:

    rs!dfield = Null

  7. Change the line to either:

    rs!dfield = #12/30/1899#

    -or-

    rs!dfield = 0

    and rerun the application.
  8. Open the ztest table in Visual FoxPro to verify the date is now blank.


REFERENCES

Keywords: kb32bitonly kberrmsg kbprb kbprogramming KB168837