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标题: 在不同的开发语言中使用ADO
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Implementing ADO with Various Development Languages
The ADO Rosetta Stone

Don Willits
Microsoft Data Access Group

July 1998

Part One: Getting Started with ADO

Part Two: ADO and COM

Part Three: Advanced Discussion and Related Information

Click to copy the sample files associated with this technical article.

Summary: Describes how to implement ADO in Microsoft Visual Basic for
Applications, Visual C++, VBScript, JScript, and Java. (56 printed pages)
Covers:

Getting started with ADO and COM

The ADO type library

COM data types

Error handling

#import
Introduction

Microsoft? ActiveX? Data Objects (ADO) is a language-neutral object model that
is the keystone of Microsoft's Universal Data Access (UDA) strategy. Because it
is language neutral and accommodates a variety of development languages, it is
difficult to present the practical usage for each environment. This article is
a discussion of the complexities inherent to using ADO within various languages
and implementation mechanisms within those languages.

To facilitate this discussion of ADO, take a lesson from the Rosetta Stone, a
slab of black basalt that provided scholars with their first significant key to
deciphering ancient Egyptian hieroglyphics. The Rosetta Stone was discovered in
1799 and appeared to contain one message (a group of priests praising their
rulers for eliminating overdue taxes in the year 196 B.C.) in three languages:
Greek, demotic characters, and Egyptian hieroglyphics. Because scholars knew
Greek, they enthusiastically attempted to use the Rosetta Stone to decipher the
hieroglyphics. Twenty years later, French scholar Jean Champollion produced a
dictionary of Egyptian hieroglyphics after rigorous comparison of the
hieroglyphics to the Greek.

In the spirit of Champollion's accomplishment, the following pages describe how
to implement ADO applications using Microsoft Visual Basic? for Applications
(VBA), Microsoft Visual C++?, Java, Microsoft Visual Basic, Scripting Edition
(VBScript), and Microsoft JScript. In this case, VBA is the "Greek text"; you
can use it as the base from which to learn about the other languages.

Numerous code listings are included in the text, as well as two sets of code
examples in an accompanying zip file. The first set contains all the code
listings presented in this document within working projects built with
Microsoft Visual Studio? 97 and the Microsoft Data Access version 2.0 software
development kit (SDK), which includes ADO 2.0. In each of these examples, you
will find files named "LISTING," which contain the actual code samples. The
second set, the Rosetta Stone samples, implement several common ADO scenarios
and are ported to a variety of development languages and environments.

The article was written against ADO 1.5 and ADO 2.0 using Visual Studio 97.
Updates will be provided, as appropriate, for new features introduced with
subsequent releases of either product. The latest version of this article is
available at www.microsoft.com/data.

This article does not discuss the ADO object model or its objects, methods,
properties, or syntax. If you are not already familiar with ADO, refer to the
ADO documentation for more information.

COM as the Heart of ADO Development

Microsoft's Component Object Model (COM) is central to all ADO development.
When you use ADO, you use COM, regardless of the language you have chosen for
the application. In particular, ADO is an Automation server, and you use COM to
invoke and utilize ADO objects.

Some languages hide the implementation details of COM more than others do, so
you don't need more than a beginner's understanding of COM to proceed. However,
as your expertise with COM grows, so does your ability to use ADO efficiently
and with more complexity. Microsoft Visual Basic for Applications (VBA) hides
many of the details of COM development, so you might choose VBA for your ADO
applications. Visual C++, Java, and Web-based scripting do not provide as much
native COM support, but they do offer you more low-level control than what you
might find with VBA.

The following are key areas of COM that you might want to be familiar with. In
addition to understanding foundational COM concepts, these subjects directly
affect your ability to develop an ADO application:

How the language or implementation you are using allows you to manipulate COM
objects.

The fundamentals of implementing a COM-based application within your chosen
language or development environment.

The ability to read a type library and, with it, how collections are used
within ADO.

Using and manipulating COM data types, specifically Bstr, Variant, and
SafeArray.

Handling error conditions via ADO.
For more information about these topics, see parts two and three.

For developers new to both COM and ADO, it may seem like a double learning
curve to get started with ADO. This is true, but once you master the COM
fundamentals needed for ADO, you are ready to implement applications utilizing
other COM components. As you are learning ADO techniques, try them first in VBA,
and then try them in Visual C++ or Java. This will help you determine whether
any difficulties you encounter are in your understanding of COM or ADO.

? 1999 Microsoft Corporation. All rights reserved. Terms of use.

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