Article #16333: Accessing Paradox Tables on CD or Read-Only Drive

 Technical Information Database

TI1333D.txt   Accessing Paradox Tables on CD or Read-Only Drive
Category   :Database Programming
Platform    :All
Product    :Delphi  All

Description:
This Technical Information document will step through the concepts 
regarding accessing Paradox tables which are located on a CD-ROM or 
any read-only device.

The Paradox locking scheme requires the existence of a PDOXUSRS.LCK 
file to handle its locking logic. This file is generally created at 
run-time and resides in the directory which also contains the tables. 
However, with a CD-ROM there is not a way to create this file at 
run-time on the CD-ROM. The solution is simple, we create this file 
and put it on the CD-ROM when the CD is pressed. The following steps 
will give you a very simple utility program for creating the 
PDOXUSRS.LCK file which you will then copy to the CD-ROM image.

1. Starting with a blank project add the following components: TEdit, 
TButton and TDatabase. 


2. In the OnClick event for the button use the following code:

procedure TForm1.Button1Click(Sender: TObject);
begin
  if ChkPath then
    Check(DbiAcqPersistTableLock(Database1.Handle,
               'PARADOX.DRO','PARADOX'));
end;


3. The ChkPath function is a user defined method of the form. It will 
simply check the path entered in the Edit box and make sure it exists. 
Here is the function:

function TForm1.ChkPath : Boolean;
var
  s : array[0..100] of char;
begin
  If DirectoryExists(Edit1.Text) then begin
    DataBase1.DatabaseName:= 'TempDB';
    DataBase1.DriverName:= 'Standard';
    DataBase1.LoginPrompt:= false;
    DataBase1.Connected := False;
    DataBase1.Params.Add('Path=' + Edit1.Text);
    DataBase1.Connected := TRUE;
    Result := TRUE;
  end
  else begin
    StrPCopy(s,'Directory : ' + Edit1.text + ' Does Not Exist');
    Application.MessageBox(s, 'Error!', MB_ICONSTOP);
    Result := FALSE;
  end;
end;

{ Note: Don't forget to put the function header in the public section 
        of the form.}


4. There is one more thing you need to add before compiling, in the 
Uses statement at the top of the unit add the following units: 
  Delphi 1.0: FileCtrl, DbiProcs, DbiTypes, DbiErrs.
  Delphi 2.0: FileCtrl , BDE


When you have compiled and executed the utility program, it will 
create two files in the directory you specified. The two files created 
are: PDOXUSRS.LCK and PARADOX.LCK. 

Note: The PARADOX.LCK file is only necessary when accessing Paradox for 
DOS tables so you can delete it. 


5. The only thing left for you to do is copy the remaining file 
(PDOXUSRS.LCK) to the CD-ROM image. Of course your tables will be 
Read-Only. 

Note: If you want to clean up this utility for future use, you can 
change the text property of the Edit box to be some default directory 
and change the Caption property of the Button to be something more 
meaningful.


Here is the final version of the code:

unit Unit1;

interface

uses
  Windows, Messages, SysUtils, Classes, Graphics, Controls, 
  Forms, Dialogs,  DB, StdCtrls, FileCtrl,

  {$IFDEF WIN32}
    BDE;
  {$ELSE}
    DbiProcs, DbiTypes, DbiErrs;
  {$ENDIF }


type
  TForm1 = class(TForm)
    Edit1: TEdit;
    Button1: TButton;
    Database1: TDatabase;
    procedure Button1Click(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
    function ChkPath : Boolean;
  end;

var
  Form1: TForm1;

implementation

{$R *.DFM}

function TForm1.ChkPath : Boolean;
var
  s : array[0..100] of char;
begin
  If DirectoryExists(Edit1.Text) then begin
    DataBase1.DatabaseName:= 'TempDB';
    DataBase1.DriverName:= 'Standard';
    DataBase1.LoginPrompt:= false;
    DataBase1.Connected := False;
    DataBase1.Params.Add('Path=' + Edit1.Text);
    DataBase1.Connected := TRUE;
    Result := TRUE;
  end
  else begin
    StrPCopy(s,'Directory : ' + Edit1.text + ' Does Not Exist');
    Application.MessageBox(s, 'Error!', MB_ICONSTOP);
    Result := FALSE;
  end;
end;

procedure TForm1.Button1Click(Sender: TObject);
begin
  if ChkPath then
    Check(DbiAcqPersistTableLock(Database1.Handle,
               'PARADOX.DRO','PARADOX'));
end;

end.


Reference:


7/16/98 4:34:09 PM
 

Last Modified: 01-SEP-99