Client Data Set in Detail11

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Deploying Applications that useClientDataSets

By: Cary Jensen

Abstract: Depending on what you do within your application, if you use one or more ClientDataSets

you may need to deploy one or more libraries, in addition to your application's executable. This

article describeswhen and how.

I've discussed a number of ClientDataSet topics in the articles that have appeared in this series, but I

have not said much about how to deploy applications that use ClientDataSets. Now that I think about

it, this is a topic that I should have covered earlier, but as the old saying goes, better late than never.

The fact is, if you include even one ClientDataSet in your application, you need to take at least oneadditional step in order to deploy that application to another machine. Fortunately, the step is pretty

simple. You either have to deploy an additional library with your application, or you have to manually

add the MidasLib unit to your project's uses clause.

To best understand this, let's create a simple application that includes a ClientDataSet, and then look

at the modules that get loaded when you run it. Use the following steps:

Create a new project, and add a ClientDataSet to your main form.1.

Set the FileName property of the ClientDataSet to a local ClientDataSet file. For example, set it

to the customer.cds file. If you installed Delphi using the default directory locations, this file can

be found in c:Program FilesCommon FilesBorland SharedData. Under Kylix, this file is located in

the demos/db/data directory under where Kylix is installed.

2.

Set the ClientDataSet's Active property to True.3.

Run your application.4.

Select View | Debug Windows | Modules to display the Modules window. If you are running

Windows, your Modules window will look similar to that shown in the following figure.

5.

loying Applications that use ClientDataSets http://dn.codegear.com/print/2929

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If your Modules window is empty, your integrated debugger is probably disabled. Select Tools |

Debugger Options, and then enable the Integrated Debugger checkbox to turn your integrated

debugger back on. You will then need to recompile and run your application.

Notice the last entry in this figure, midas.dll. Midas.dll is the DLL (dynamic link library) under Windowsthat contains the routines that a ClientDataSet needs. These routines are required anytime you

activate a ClientDataSet, whether you are using it with local files, as in this case, or any other way.

For example, if you are simply using a ClientDataSet to store data temporarily in memory, it will also

need access to these routines.

If you are using Kylix, the ClientDataSet relies on a shared object library named libmidas.so.1.

(Actually, libmidas.so.1 is a symbolic link. In Kylix 2, this file is symbolically linked to libmidas.so.1.0.)

This is shown in the following figure.


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I must admit that I think the Modules window is one of the more important in the IDE (integrated

development environment). This window displays all libraries that your application has loaded,

including ActiveX servers (under Windows). I make a habit of checking the Modules window before I

deploy an application. This way I can verify that I will deploy all libraries required by my application.

When you installed Delphi (or Kylix), the installer also installed the midas library. As a result, if youcreate an application that employs a ClientDataSet and run it only on your development machine, that

library is already available. If you need to distribute this application you may also need to deploy this

library to a location where the application can find it. Under Windows, you will likely install this library

in the Windows system directory (or system32). With Kylix, you may need to install this file to the

location pointed to by the LD_LIBRARY_PATH environment variable.

Deploying Applications Without the Midas Library

You may have noticed that in the preceding paragraph I was equivocal about the need to install the

midas library. This is because there is a simple step that you can take that will make deployment of

this library unnecessary. Specifically, if you add the MidasLib unit to your project's uses clause, your

application will link all of the routines required by the ClientDataSet into your executable. As a result,the midas library will not be loaded at runtime, and therefore does not need to be deployed.

You can demonstrate this easily. Take the project you created by following the steps given earlier in

this article, and add MidasLib to your project's uses clause. When you are done, your project source

will look something like the following.

program Project1;

uses

MidasLib,

Forms,

Unit1 in'Unit1.pas'{Form1};

{$R *.res}

begin

Application.Initialize;

Application.CreateForm(TForm1, Form1);


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Application.Run;

end.

If you now run your application again, and then display the Modules window, it will look something

like this.

As you can see, the DLL midas.dll is not listed in this window, which means that it is no longer being

loaded by the application.

Why Not Always Use MidasLib

I'll bet you're wondering why you don't simply included MidasLib in the uses clause of all of your

applications that use ClientDataSets. The reason is that using the MidasLib unit increases the size of

your executable. Not by much, but it does increase its size.

How much? Well, that's easy to test. Once you compile your application, you can view the Information

dialog box to get some basic statistics about the compiled executable, including its overall file size. To

display this dialog box, select Project | Information for Project from Delphi's main menu. For example,

the following figure shows this dialog box after compiling the simple application created earlier in this

article, prior to adding MidasLib to the project's uses clause.


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Displaying this dialog box again after adding MidasLib to the project's uses clause and recompiling

shows that the executable has grown in size, as shown here.

The difference is a little over 200 K bytes.

There is another issue that applies when you are using Delphi. If you deploy two or more applications

that make use of ClientDataSets, and you install midas.dll in a shared directory, when those

applications are running at the same time they will use only one copy of the DLL in memory, using

less RAM overall. Again, it's not much of a savings, but it is a savings.

Under Linux, shared libraries are not shared in memory. Each instance of the library is loaded into its

own process. (They are called shared libraries because two or more applications can share the same

file on disk.) As a result, this same savings in RAM is not realized when two or more Kylix applications

that use ClientDataSets are running simultaneously.

My recommendation? Personally, I prefer to include MidasLib in my project's uses clause. This way I

avoid potential problems associated with external DLLs, such as their being overwritten by otherapplications. It also makes deployment just a little bit easier.

About the Author

Cary Jensen is President of Jensen Data Systems, Inc., a Texas-based training and consulting company

that won the 2002 Delphi Informant Magazine Readers Choice award for Best Training. He is the

author and presenter for Delphi Developer Days (www.DelphiDeveloperDays.com), an information-

packed Delphi (TM) seminar series that tours North America and Europe, and Delphi Developer Days

Power Workshops, focused Delphi (TM) training. Cary is also an award-winning, best-selling co-author

of eighteen books, including Building Kylix Applications (2001, Osborne/McGraw-Hill), Oracle

JDeveloper (1999, Oracle Press), JBuilder Essentials (1998, Osborne/McGraw-Hill), and Delphi In

Depth (1996, Osborne/McGraw-Hill). For information about onsite training and consulting you cancontact Cary at [email protected], or visit his Web site at

www.JensenDataSystems.com.

Click here for a listing of upcoming seminars, workshops, and conferences where Cary Jensen is


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presenting.

Breaking News: Get hands-on training with Cary Jensen. Jensen Data Systems, Inc. is proud to

announce Delphi Developer Days Power Workshops, focused Delphi (TM) training. These intense,

two-day workshops give you the opportunity to explore and implement a variety of Delphi techniques

with Cary Jensen, one of the world's leading Delphi experts. Workshop topics include ClientDataSet,

IntraWeb, and more. Due to the hands-on nature of these workshops, class size is very

limited. Reserve your seat now.Click here for more information about Delphi Developer Days

Power Workshops, or visit http://www.DelphiDeveloperDays.com.

Copyright ) 2002 Cary Jensen, Jensen Data Systems, Inc.

ALL RIGHTS RESERVED. NO PART OF THIS DOCUMENT CAN BE COPIED IN ANY FORM WITHOUT THEEXPRESS, WRITTEN CONSENT OF THE AUTHOR.

Published on: 11/24/2002 9:34:14 AM

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Client Data Set in Detail11