Q148917: How to Use the DAO Dynaset with Microsoft SQL Server 6.0

Article: Q148917
Product(s): Microsoft C Compiler
Version(s): 4.00
Operating System(s): 
Keyword(s): kbDAOsearch kbDatabase kbMFC kbVC
Last Modified: 03-AUG-2001

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The information in this article applies to:

- The Microsoft Foundation Classes (MFC), included with:
   - Microsoft Visual C++, 32-bit Editions, version 4.0 
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SUMMARY
=======

You can use CDaoRecordset to insert, update, or delete records in a table in a
Microsoft SQL Server 6.0 database. There are two ways to do it:

- Use a direct ODBC connection in CDaoDatabase::Open(). In this case, there
  must be a unique index on one of the fields in the recordset. If there is no
  such index, the recordset will become read only.

-or-

- Use a linked table through a Microsoft Access 7.0 database. You must have a
  unique index on one of the fields in the recordset. Microsoft Access asks for
  a unique identifier while creating the linked table if the table does not
  have a unique index. If you do not specify a field as the unique identifier
  and there is no unique index, the recordset will become read only.

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

Using a Direct ODBC Connection in CDaoDatabase::Open()
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If you create a DAO dynaset without specifying a unique index on one or more
fields in the recordset and then try updating or adding a record, MFC DAO will
throw an exception and you will see the following errors in the MFC Trace
output:

AddNew fails with this message:

  

  DAO Call Failed.
  m_pDAORecordset->AddNew()
  In file daocore.cpp on line 4498
  scode = 800A0BD3

  Error Code = 3027
  Source = DAO.Recordset
  Description = Can't update. Database or object is read-only.

Edit() fails with a similar message:

  

  DAO Call Failed.
  m_pDAORecordset->Edit()
  In file daocore.cpp on line 4525
  scode = 800A0BD3

  Error Code = 3027
  Source = DAO.Recordset
  Description = Can't update. Database or object is read-only.

Using a Linked Table Through a Microsoft Access 7 Database
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If you create a DAO dynaset on a linked table in Microsoft Access, the recordset
becomes read only if there is no unique identifier specified in Microsoft Access
and there is no unique index on some field(s) in the recordset. You will see the
same error messages from AddNew or Edit as shown in the previous case.

One way to satisfy the requirement for a unique index is to create an index on
the primary key. Note that if you use the PRIMARY KEY specification new to SQL
Server version 6.0 when creating your tables, you will automatically generate a
unique index on the primary key. This syntax is demonstrated here:

  CREATE TABLE MyTable
         (column1 CHAR(10) PRIMARY KEY NOT NULL,
          column2 CHAR(10))

Additional query words: kbinf 4.00

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Keywords          : kbDAOsearch kbDatabase kbMFC kbVC 
Technology        : kbAudDeveloper kbMFC
Version           : 4.00

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