VCL/CLX Developers Guide

Record/Row Locking

sdk\ctree.vcl.delphi\tutorials\Tutorial3.pas

Now we will explore row/record locks using the FairCom DB CodeGear VCL ISAM Component Framework - Delphi.

The functionality for this tutorial focuses on inserting/adding rows/records, then updating a single row/record in the customer master table under locking control. The application will pause after a LOCK is placed on a row/record. Another instance of this application should then be launched, which will block, waiting on the lock held by the first instance. Pressing the <Enter> key will enable the first instance to proceed. This will result in removing the lock thereby allowing the second instance to continue execution. Launching two processes provides a visual demonstration of the effects of locking and a basis for experimentation on your own.

As with all other examples in the c-tree tutorial series, this tutorial simplifies the creation and use of a database into four simple steps: Initialize(), Define(), Manage(), and you’re Done() !

Tutorial #3: Locking

Here we demonstrate the enforcement of data integrity by introducing record/row "locking".

• Initialize() - Connects to the FairCom Database Engine.
• Define() - Defines and creates a "customer master" (custmast) table/file.
• Manage() - Adds a few rows/records, manipulates them, and displays the results.
• Done() - Disconnects from FairCom Database Engine.

Note our simple mainline:

procedure TForm1.FormShow(Sender: TObject);

begin

Initialize;

Define;

Manage;

end;

procedure TForm1.FormCloseQuery(Sender: TObject; var CanClose: Boolean);

begin

CanClose := true;

Done;

end;

We suggest opening the source code with your own editor.

Continue now to review these four steps.

In This Section Init Define Manage Done Additional Resources