unit OoTable; {Object Oriented Table. At least I think so..}



{ Author: Michael Ax

  Copyright (c) 1995 Michael Ax.  All Rights Reserved.

  This source code may be used and modified by anyone with a license to

  WebHub or TPack from HREF Tools Corp. Obtain purchasing and additional

  information by sending an email to to software@href.com (any subject,

  any message)... or visit us on the web at http://www.href.com/software/



  Send eMail to code@href.com for technical support.

}



{we're going to create a property that represents the current record's unique id }



interface

uses db, dbtables;



type

  TTableUniqueIDField=class(TTable)

  private

    fUniqueID: TField;

    {making this a pointer to the tField rather than an index keeps things simple and fast}

  protected

    function GetUniqueID:LongInt;

    procedure SetUniqueID(aValue:LongInt);

  public

    procedure DoAfterOpen; Override;

  published

    property UniqueID: LongInt read GetUniqueID write SetUniqueID stored false;

    end;  {modified but not tested as published in this sample}



  {note: while you could make this a component you probably'd want to define individual

  components for every major table in the system vis inheritance.. but that get tricky if

  you want tables to know about each other. otoh you can create new instance of tables

  easy if they have a type. you can set table names in the Create procs so that you can

  instantiate and open them without knowing a tablename or alias!..}



  TCustomerTable= class(TTableUniqueIDField); {that's enough to get an alias type for this}



const

  cUniqueID='UniqueID'; {reference to the field name. use a stringtable resource!}



implementation



procedure TTableUniqueIDField.DoAfterOpen;

begin

  inherited DoAfterOpen;

  fUniqueID:=FieldByName(cUniqueId); {raises exception if not there}

  fUniqueID.ReadOnly:=True;          {user can not change the field}

end;



procedure TTableUniqueIDField.SetUniqueID(aValue:LongInt);

begin

  if State<>dsInactive then

    with fUniqueID do begin

      ReadOnly:=False;               {gain access}

      AsInteger:=aValue;             {set}

      ReadOnly:=True;                {restrict access} {without passwording things}

      end

end;



function TTableUniqueIDField.GetUniqueID:LongInt;

begin

  if State<>dsInactive then

    Result:=fUniqueID.AsInteger

  else

    Result:=-1;

end;



end.