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Q132397: HOWTO: Retrieve a Counter Field Value Without Requerying

Article: Q132397
Product(s): Microsoft C Compiler
Version(s): 
Operating System(s): 
Keyword(s): 
Last Modified: 30-AUG-2001

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The information in this article applies to:

- The Microsoft Foundation Classes (MFC), included with:
   - Microsoft Visual C++ for Windows, 16-bit edition, version 1.52 
   - Microsoft Visual C++, 32-bit Editions, versions 2.1, 2.2, 4.0 
   - Microsoft Visual C++, 32-bit Enterprise Edition, version 5.0 
   - Microsoft Visual C++, 32-bit Professional Edition, version 5.0 
   - Microsoft Visual C++, 32-bit Enterprise Edition, version 6.0 
   - Microsoft Visual C++, 32-bit Professional Edition, version 6.0 
   - Microsoft Visual C++, 32-bit Learning Edition, version 6.0 
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SUMMARY
=======

The Microsoft Access ODBC driver version 2.x or higher provides a Counter field
data type. This is an autoincrement field, meaning that the value of the field
is assigned automatically by the ODBC driver when a record is first created.
This value can then be used as a primary key or as general index.

Once a record is added, the value of the counter field is assigned by the
Microsoft Access ODBC driver version 2.x or higher. You can save this value for
later use, and have an application retrieve the value of the counter field
without re-querying. This article explains how.

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

ODBC doesn't supply any mechanism by which an application can easily retrieve
the value of an autoincrement field when a record is added. However, the
Microsoft Access ODBC driver version 2.x or higher does provide a feature that
can help. The Microsoft Access ODBC driver version 2.x or higher appends newly
added records to the end of the current recordset if you use a dynaset. After
adding a record, an application can call MoveLast() to move to the last record
of the recordset to retrieve the value of the new record.

If you want to move back to the previous cursor position following the MoveLast()
call, use the information provided in the following article in the Microsoft
Knowledge Base:

  Q132398 HOWTO: Use Bookmarks with the MFC ODBC Database Classes

Sample Code
-----------

The following code segment is an example of how to use the bookmark code in
article Q132398 to retrieve the value of a counter (autoincrement) field in
Microsoft Access version 2.0 or higher database so that you can save the value
for later use within your application. This example moves to a record, gets the
bookmark for the record, adds a record, calls MoveLast() to get to the newly
added record and thus retrieve the counter field value, and then moves back to
the record it came from.

     CDatabase db;
     db.Open("MYDataSourceName",NULL,NULL,"ODBC;",FALSE);
     CCounterSet rs(&db);

     // Open up dynaset because any records added by a CRecordset using
     // dynasets are appended to the end of Microsoft Access 2.0 or higher
     //recordset

     rs.Open(CRecordset::dynaset);

     // move to some record
     rs.MoveNext();

     BOOKMARK bookmark;
     rs.GetBookmark(&bookmark);

     // Add record. Counter field of record will be given a value by
     // the ODBC driver
     rs.AddNew();
     rs.m_textfield="SomeText";
     rs.Update();

     // MoveLast to get on record just added
     rs.MoveLast();

     // retrieve the value of the counter field for the
     // newly added record here

     // return to the record you were on
     rs.MoveToBookmark(bookmark);

Additional query words: kbVC150 kbVC151 MfcDatabase kbMFC kbVC152 kbVC210 kbVC220 kbVC400 kbVC500 kbVC600 kbODBC

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Keywords          :  
Technology        : kbAudDeveloper kbMFC
Issue type        : kbhowto

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