EXPRESS OLE DB Library for C++

Library Class Hierarchy

Overview

In my last article, I showed how to extend an OLE DB consumer template class and make it much easier to use in applications. I had also explained how you can utilize the power of C++ exception-handling feature to make your work easier, especially in error handling. It was just a small class in my last article.

In this article, I will present a complete library that is feature-rich, light-weight, lightening fast, and most easy to use. But, before you undestand how to use the library, you have to gain some background knowledge. So,, let us start gaining that knowledge. 

THE DILEMMA OF DATA ACCESS

When it comes to choosingthe right data access technology for application development, most Visual C++programmers face a puzzling set of choices. On one hand, these choices arelimited and on the other hand, they are conflicting in terms of performancerequirement and ease of use. Whether it is a stand-alone application, aclient/server application or a web application, a C++ programmer would neverlike to compromise the factors of decision such as performance, speed, and resourcemanagement. The simple reason for this fact is the underlying tenet that theC++ programmers are supposed to churn out some smartest applications in theprogramming world. Although the type and make of the database as well as thenature of application can largely influence the decision, it is not as easy asit seems.

Let us try to understand and analyze some of themost obvious data access choices:

Native Library :

Native libraries aresupplied by many database vendors and they provide fastest data access for therespective databases. However, due to the well-known fact that the code writtenusing a native library is not portable to other databases, your applicationgets locked into the database vendors technology. Moreover, each nativelibrary is totally different in nature compared to other libraries. So, we willnot devout any time discussing this option in detail and leave it to thedevelopers to explore further on this topic.

ADO :

Since its introduction, ADO has been the most widely used option for data access onWindows platform. Though primarily designed and developed for Visual Basic andscripting languages, it is not used less in Visual C++ world either. AfterODBC, ADO is the major library that is proven and tested for data access on Windowsplatform. Thousands of developers using various programming languages onwindows platform heavily rely on ADO for the data access need of theirapplications. Having said that, you might wonder why ADO is not an ideal choicefor Visual C++ developers. Well, Hereis why:

• ADO is designed keeping in mind the automation-based languages. So, everything it speaks is in terms of VARIANT, a data type that is hated most by C++ developers. When it comes to using VARIANTs and BSTRs, C++ developers get a hitch. The reason for this disliking is clearly understandable. Converting a VARIANT to and from the native data types of C++ is really a pain. Not only does it call for extra work, but also it affects the overall performance of the application.

• ADO is a set of wrapper classes that are built on top of OLE DB interfaces. So, it puts an extra layer as far as C++ is concerned since OLE DB interfaces can be directly accessed through C++. Theoretically, an application that uses OLE DB interfaces is considerably faster than the one that uses ADO.

• Using ADO in Visual C++ also comes with other drawbacks and limitations.

  • If you use #import statement, you cannot avoid jump-to-exception situation even if you want to avoid it. Additionally, you loose flexibility of having default arguments to the methods. You must provide all method arguments.

  • If you use ADO SDK or raw COM interfaces, you have to check for HRESULT values at each and every point. Since data access code normally requires frequent method calls, it becomes cumbersome to check these values.

Concluding on all the points mentioned above, we could say that ADO should be the choice of dataaccess for C++ programmers only if there is no better choice than that.

OLE DB Consumer Templates :

To overcome thelimitations of using ADO in C++, Microsoft provided OLE DB consumer templatesfor C++ developers. Like ADO, they are a set of template classes that are alsobuilt around OLE DB interfaces. However, unlike ADO, these classes put only athin layer on OLE DB and therefore they are lighter, faster, and much powerful.Besides, consumer templates make a native C++ class library, i.e., it is a pureC++ class library and hence it uses the native C++ data types. So, using theseclasses eliminate the need for using VARIANTs or BSTRs.

Putting all these facts together, one can easilyconclude that OLE DB consumer classes have an edge over ADO. Yes, theydefinitely have. You might wonder then why in the world would any C++programmer use ADO at all. Adding to your wonder is the fact that more C++developers use ADO in their applications than OLE DB consumer templates. But,wait a minute. There are several good reasons for this fact. Let us see. I amgoing to list a few of these reasons below.

• Memory leaks & bugs : The OLE DB consumer templates contain several classes with bugs and memory leak problems. Most notable of them are the methods of CDataSource class that leak memory and the column binding in CDynamicAccessor class that does not handle wide characters properly. As of Service Pack 5 of Visual Studio 6.0, these problems are not fixed.

• Lack of features and flexibility : Although consumer templates are much easier to use than raw OLE DB interfaces, they lack several features and functionalities compared to ADO. Checking EOF/BOF status in a rowset, handling BLOB data, refreshing and updating a rowset, fetching error details from HRESULT values are just a few of them to list. Using a data access library without these features in your application is a big work in itself.

• Error reporting : Most methods of consumer template classes return some HRESULT value. Getting error details from these values requires a fair amount of effort, especially if you want to get the error messages from database server. There is no easy shortcut in consumer templates to do this.

• Lack of XML support : There is no XML support so far in the consumer template classes. Looking at the .NET version of Visual C++, it seems like Microsoft is planning to incorporate XML support in .NET consumer templates. But till then, you have to resort to your own knowledge of database and XML if you use consumer templates.

• Cryptic and sparse documentation : If you have moved from ADO to consumer templates, you would find the documentation of consumer templates suffocating. The documentation provided in MSDN is short and sparse and very limited in terms of providing examples and samples. In addition to all these facts, there is hardly any good book in market on OLE DB consumer classes that provides the complete coverage of all the classes.

• Binding to controls : Unless you are writing a middleware component or a web application, you need to display your data in some form of GUI components. It could be as simple as a text box or as complex as a compound spreadsheet grid. In any case, you need to bind your data to the user interface at some point of time in your application development cycle. Most commercial controls provide data-binding support for ADO. However, since consumer templates are a low-level interface to data, the binding responsibility is rested upon the developer. And binding data to a control is not as simple as point-and-click. This is the reason why many developers choose to convert their OLE DB rowset data into ADO Recordset object for displaying them in GUI.

• Steeper learning curve : Using OLE DB consumer templates for such basic tasks as inserting and deleting rows from a database table is not a problem. However, if you want to move little above that level, you need to understand well the nitty-gritty of OLE DB. As for example, if you want to create an updateable client-side cursor, not only a lot of work is needed, but also the firm understanding of OLE DB interfaces is must. The fact remains that no matter what technology you use, if you want to access databases at lower level, there is no easy way. And consumer templates are no exception.

INTRODUCTION TO EXPRESS OLE DB LIBRARY

Considering allthe aforementioned issues about ADO and consumer templates, the fact becomesclearer that there is no panacea for C++ programmers as far as data access isconcerned. No single library is both sufficient as well as efficient. Althoughconsumer template classes are excellent tool for accessing databases, they areincomplete in feature and insufficient from an application development point ofview.

EXPRESSOLE DB is a C++ class library that extends the OLE DB consumer template classesand is a complete, feature-rich, and extremely powerful data access solutionfor C++ programmers. It is built with the aim of eliminating the limitationsand drawbacks of consumer templates while still retaining power and performanceof consumer templates. Some of the features of this library can be summarizedbriefly as follows:

• Easy to use : The library is designed to be as developer-friendly as possible. An attempt is also made to make it as simple as possible.

• Easy to learn : Many of the features of this library are modeled after ADO and, as such, it is extremely intuitive. The bottom line is that if you know the basics of any data access library, you can easily learn this one too.

• Easy to debug : Several debug macros and validations are embedded in almost every method in this library. This fact makes a big difference as far as application debugging is concerned. Frequently, it is much easier to debug an application written using EXPRESS OLE DB than the one written using ADO.

• High performance : Although so many features are added to the library and a lot of care is taken to avoid errors as far as possible, a big effort is made to keep it lightweight and reduce unnecessary overhead. Basic benchmark tests show that a performance gain of EXPRESS OLE DB library over ADO range from 20% to 200% depending upon various factors.

• Rich in features : We have seen that consumer template classes lack several functionalitiesand features that are necessary for such basic database operations as checkingfor EOF, counting rows in arecordset, checking data type of a column etc. So, almost all of these features are added in EXPRESS OLE DB.

• XML support : EXPRESS OLE DB provides built-in support for XML. Using this library, you can extract the column structure as well as any data from any source in XML format.

• Powerful Error-Trapping : Automatic error-trapping mechanism is provided through exception handling and a powerful error object can be used to analyze and extract various types of errors.

• Flexibility : The biggest advantage offered by this library is the flexibility it offers. Take an example of error trapping. You have three different ways to control errors: exceptions, error object, and custom class.

• Integration : The Express OLE DB library is currently integrated with other commercial libraries such as RogueWave. Stingray studio's Objective Grid library. Future versions will see more integration with many other libraries from different vendors.

• Free : Above all other points, the biggest advantage is that the Express OLE DB library is absolutely freely distributed by Sypram Technology.

Since this library requires a lot of files, I have included only the sample files in this article. The complete library can be downloaded from the websitewww.sypram.com. It is distributed completely FREE for the purpose of sharing knowledge. The samples proveded here are also included as part of the class library. Moreover, the complete documentation is also bundled with the library setup. So, I am skipping the details of explanation and use of library. In case you have any technical question on this library, you may [e-mail]

Downloads

Download source - sample projects - 298 Kb
Library file - Part 1 - 1,205 kb
Library file - Part 2 - 1,090 kb