Record/Row Locking

..\sdk\sql.dbx\Tutorial3\Unit1.pas

Now we will explore row/record locks using the c-treeACE SQL DBX Component - 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.

Like 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 c-treeACE Database Engine.
• Define() - Defines and creates a "customer master" (custmast) table/file.
• Manage() - Adds a few rows/records; Reads the rows/records back from the database; displays the column/field content. Then demonstrates an update operation under locking control, and a scenario that shows a locking conflict.
• Done() - Disconnects from c-treeACE Database Engine.

Note our simple mainline:

procedure TForm1.FormShow(Sender: TObject);

begin

    Initialize;

    Define;

    Manage;

end;

procedure TForm1.BtnCloseClick(Sender: TObject);

begin

    Done;

    Close;

end;

We suggest opening the source code with your own editor.

Continue now to review these four steps.