Introduction

VO2Jet is a Visual Objects Class Library that gives VO developers an efficient and easy to use interface to Microsoft Access databases. The Class library includes a set of early bound OLE classes that talk directly to the Microsoft Jet engine, the engine behind the Microsoft Access databases. It also has a higher level DbServer compatible DataServer class that allows VO developers to use the data from Microsoft Access databases in combination with the VO DataWindow and Databrowser classes.

What is new in version 2.8:

•	Version 2.801 of Vo2Jet has been changed to work successfully with VO 2.8

What is new in version 2.721:

•	Version 2.721 of Vo2Jet has been changed to work successfully with VO 2.7b1 (VOPS Build)

What is new in version 2.72

•	Version 2.72 of Vo2Jet has been changed to work successfully with VO 2.7b

What is new in version 2.71:

•	Version 2.71 of Vo2Jet has been changed to work successfully with VO 2.7a

What is new in version 2.70:

•	Version 2.7 of Vo2Jet has been changed to work successfully with VO 2.7

What is new in version 2.60:

•	Version 2.6 of Vo2Jet is recompiled for VO 2.6, and includes a couple of bug fixes and new features. See the change history for more information

•	The library by default now runs in Jet 4 mode. To change to Jet 3.5 mode you have to call DaoEnableVersion36(FALSE)

•	The Jet Server editor now automatically switches to a different operating mode when the correct DAO version is not available.

•	A couple of other changes. See change history.

What is new in version 2.50:

•

We have added a special strongly typed version of the library.This version performs a little faster, and speed is all you want, right ? The only difference in this version is that all the Dao Objects have changed to strongly typed, so there are no optional parameters anymore. If you use this library and get compiler warnings about missing arguments, just supply enough NIL values.

•

We have added a Classmate compatible version of the library. The only difference in using is that the DataServer classes in this library start with a 'c', so DaoServer is changed to cDaoServer. There are no changes to the methods, except for the fact that everything is strongly typed, so there are no optional parameters anymore. There is also a sample that uses the ClassMate browser. Please check this !

•	We have added support for DAO 3.60 & Jet 4.0, so you can use our library with both version. Check the DaoEnableVersion36() function for more information.

•	We have added a JetDebugger sample, that you can link into your application to see what databases, recordsets etc. you have opened in your application.

•	We have changed the JetEditor subsystem to work with VO 2.5, including the Version Control Interface.

DAO

VO2Jet uses Data Access Objects (DAO), a rich hierarchy of OLE classes that Microsoft supplies for natively interfacing with Access databases on 32-bit platforms (Windows 95 and Windows NT 3.5 and higher). Before using VO2Jet, you must ensure that a copy of DAO (version 3.5 or later) is installed on your computer. DAO may already be installed if you are using Microsoft Office, Microsoft Access, Microsoft Visual Basic Professional, or Microsoft Visual C++ 4.0.

Applications can communicate with the DAO OLE objects using two kinds of interfaces

•	An OLE Automation interface for use with OLE automation clients such as Visual basic, Visual Objects and other development languages. This interface is easy to use, but not so very fast.

The reason this interface is not very fast is because it is late bound, and all arguments are passed as variants (the OLE equivalent of the VO Usual data type). At run time when you call a method the method name must be looked up and the arguments must be converted from their VO data type into variants and back to the data types that DAO needs on the other side.

When you generate classes using the Ole Automation Server wizard inside VO, part of this speed problem is resolved, because method names are converted to their numeric identifiers, but still the conversion of the data types is necessary.

•

A COM interface designed for use with compiled languages such as Visual C++ and Visual Objects, where speed is very important. With these interfaces all COM calls are early bound, and the arguments to the methods are passed in the data type that the DAO classes expect, so no conversion is necessary.

For speed reasons VO2Jet uses the COM interface in stead of the slower OLE Automation interface. The performance of the classes is this way 5 to 10 times faster than using OLE Automation.

About this Helpfile

All of the classes and functions from VO2Jet start with the DAO prefix. To make the index of the Helpfile more usable, we have omitted the DAO prefix in the topic index in this helpfile. We hope you will appreciate that.

Support

When you need support for using VO2Jet you can get that through the following ways:

•	Get in contact with your dealer

•	Send an e-mail message to support@heliks.nl

•	Post a message in the Usenet newsgroup comp.lang.clipper.visual-objects

Updates and patches

For new updates and patches look at: http://www.heliks.nl