Microsoft KB Archive/141717

= How to use MFC DAO classes to create database objects in Visual C++ =

Article ID: 141717

Article Last Modified on 6/1/2005

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APPLIES TO

 Microsoft Foundation Class Library 4.2, when used with:  Microsoft Visual C++ 4.0 Standard Edition

 Microsoft Visual C++ 4.1 Subscription

 Microsoft Visual C++ 4.2 Enterprise Edition

 Microsoft Visual C++ 4.2 Professional Edition</li></ul>

 Microsoft Visual C++ 4.2 Enterprise Edition</li></ul>

 Microsoft Visual C++ 4.2 Professional Edition</li></ul>

 Microsoft Visual C++ 5.0 Enterprise Edition</li></ul>

 Microsoft Visual C++ 5.0 Professional Edition</li></ul>

 Microsoft Visual C++ 6.0 Enterprise Edition</li></ul>

 Microsoft Visual C++ 6.0 Professional Edition</li></ul>

 Microsoft Visual C++ 6.0 Standard Edition</li></ul> </li></ul>

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This article was previously published under Q141717

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SUMMARY
The DAOTable sample (Daotbl.exe) demonstrates how to use the MFC DAO classes to create the following common database objects: databases, tables, queries, fields, and indexes. This dialog-based application maps the properties of these objects to controls the user can set or view. The program source code is organized so that most database interaction is isolated from the user interface code to ease finding examples of how to use MFC DAO.

In addition to demonstrating the use of the MFC DAO classes, this sample can be a useful tool for creating simple Microsoft Access databases. You can create .mdb files from scratch, create and delete tables and queries, add and delete fields and indexes in the tables, and modify existing queries.

The following files contain the code that performs the database operations. Additional files in the project provide the user interface and high level database manipulation. <pre class="fixed_text">  QUERYDEF.CPP, .H -- functions to create and use queries TABLEDEF.CPP, .H -- functions to create and use tables FIELD.CPP, .H   -- functions to create and use fields INDEX.CPP, .H   -- functions to create and use indexes DATABASE.CPP, .H -- functions to create and use databases To use this code and the MFC DAO classes, you must have Visual C++ 4.0 or later.

NOTE: Beginning with Visual C++ 4.1, the DAOTable sample is included with the Visual C++ CD.

Special Note for Visual C++ 4.1 Users
The DAOTABLE sample that shipped with Visual C++ 4.1 contains a bug that will prevent you from creating fields that are of any type other than text. To correct this problem, you can download the fixed sample as directed below or make the following correction to the ADDTBDLG.CPP file:

Replace this line m_FI.m_bAllowZeroLength = TRUE; with this line: m_FI.m_bAllowZeroLength = FALSE; This change will disable a workaround that was necessary to avoid a bug in Visual C++ 4.0. In the download files (DAOTBL.EXE), the workaround code is conditionally compiled depending on which version you are using to build the sample. If you do not make the correction given in this section and you run the application using the Visual C++ 4.1 DLLs, the following exception will be thrown when you try to create nontext fields:

Couldn't create field--Exception: Invalid Operation.

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MORE INFORMATION
The following files are available for download from the Microsoft Download Center:

Daotbl.exe

For more information about how to download Microsoft Support files, click the following article number to view the article in the Microsoft Knowledge Base:

119591 How to obtain Microsoft support files from online services

Microsoft scanned this file for viruses. Microsoft used the most current virus-detection software that was available on the date that the file was posted. The file is stored on security-enhanced servers that help prevent any unauthorized changes to the file.

NOTE: The file must be decompressed by typing "DAOTBL.EXE -d" to re-create the directory structure.

The MFC DAO classes provide a way to directly use the Microsoft Jet Database Engine. Although Visual C++ wizards automatically generate code that will create and open recordsets for you based on implicitly created database and workspace objects, the code they provide does not demonstrate creating and manipulating MFC DAO objects directly. With MFC DAO classes, you can create the majority of DAO objects and set their properties.

This sample demonstrates using the MFC DAO classes to create and use the following DAO objects: databases, tables, queries, fields, and indexes. Exception handling with both MFC exception macros and the C++ exception mechanism is also shown. Further, DAO exceptions are put to use in detecting the existence of objects in the DAO collections.

Listed below are all the files in the project (except those that are common to all Visual C++ projects). Each file is shown with the type of components it contains and a brief description. <pre class="fixed_text">  ADDQYDLG.CPP         - USER INTERFACE - query definition dialog ADDQYDLG.H  DAOTABLE.CPP         - APPLICATION - main application objects DAOTABLE.H  DAOTDLG.CPP          - USER INTERFACE - main dialog DAOTDLG.H  DATABASE.CPP         - MFC DAO - database specific functions DATABASE.H  ADDIXDLG.CPP         - USER INTERFACE - add indexes dialog ADDIXDLG.H  ADDTBDLG.CPP         - USER INTERFACE - table definition dialog ADDTBDLG.H  FIELD.CPP            - MFC DAO - field specific functions FIELD.H  LISTCTRL.CPP         - USER INTERFACE - derived CListCtrl class LISTCTRL.H  INDEX.CPP            - MFC DAO - index specific functions INDEX.H  QUERYDEF.CPP         - MFC DAO - querydef specific functions QUERYDEF.H  TABLEDEF.CPP         - MFC DAO - tabledef specific functions TABLEDEF.H  ADDDBDLG.CPP         - USER INTERFACE - database definition dialog ADDDBDLG.H

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