asked on

How to Evaluate a String Expression

Greetings,

I want to have a function that will check if 7 diferent tables are empty without having to specify the commands 7 times. Would be something like this:

procedure TForm1.OpenDBExecute(Sender: TObject);
var
ct : integer ;
dummys: string ;
begin
for ct := 1 to 7 do
begin
dummys := 'Form1.QAgenda' + inttostr(dummys) + '.IsEmpty';
if MyFunction( dummys) then
showmessage( 'table is empty' ) ;
end;
end;

what I want is not to have to write
if Form1.QAgenda1.IsEmpty then
...
if Form2.QAgenda1.IsEmpty then
...
if Form3.QAgenda1.IsEmpty then
...
if Form4.QAgenda1.IsEmpty then
...
if Form5.QAgenda1.IsEmpty then
...
if Form6.QAgenda1.IsEmpty then
...
if Form7.QAgenda1.IsEmpty then
...

This is a very basic question but I couldnt find the way how to evaluate the expression

Thanks for any help

shaneholmes

Something like this maybe

for I:= 1 to 7 do
if TTable(FindComponent(TTable + inttostr(I))).isEmpty
then

Shane

shaneholmes

oops

for I:= 1 to 7 do
if TTable(FindComponent(QAgenda + inttostr(I))).isEmpty
then

btw, you should create a TDatamodule, and centralize all of your tables there

then this method would work great

for I:= 1 to 7 do
if TTable(DataModule1.FindComponent(QAgenda + inttostr(I))).isEmpty
then

Shane

ROGERPORT

ASKER

Your answer pointed me in the right direction, but still cant put it to work.

The QAgenda component is of type TADOQuery

Any idea why the code below gives an access violation run time error ?

if not (TADOQuery(FindComponent('Form1.QAgenda' + inttostr(ct))).isEmpty) then
...

Though I recognise the value of you TDatamodule sugestion, is that mandatory ?

BTW where is that TDatamodule located ? is that a component ?

shaneholmes

In your IDE, from the main menu, choose

new/ DataModule

A datamodule is a non-visible form where you can place all your non-visual dataset components (TTables, TDatasources, etc)

When you have created your new datamodule, save it, then do the following

from delphi ide main menu, choose

project / view source

you should have something like this

program Project1;

uses
Forms,
Unit1 in 'Unit1.pas' {Form1},
Unit2 in 'Unit2.pas' {DataModule2: TDataModule};

{$R *.res}

begin
Application.Initialize;
Application.CreateForm(TForm1, Form1);
Application.CreateForm(TDataModule2, DataModule2);
Application.Run;
end.

you need to move the Datamodule source up above the main form

program Project1;

uses
Forms,
Unit1 in 'Unit1.pas' {Form1},
Unit2 in 'Unit2.pas' {DataModule2: TDataModule};

{$R *.res}

begin
Application.Initialize;
Application.CreateForm(TDataModule2, DataModule2);
Application.CreateForm(TForm1, Form1);
Application.Run;
end.

This will make sure your main form is the last form created and therfore shown.

Then from each unit that needs access to the tables, you just add the datamodule unit to their source as follows:

unit Unit1; //main form

interface

uses
Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
Dialogs;

type
TForm1 = class(TForm)
private
{ Private declarations }
public
{ Public declarations }
end;

var
Form1: TForm1;

implementation

uses Unit2; //datamodule unit

{$R *.dfm}

end.

Shane

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shaneholmes

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ROGERPORT

ASKER

Thanks for your valuable help. I'll change the way I am doing the application to use a datamodule.

BTW

I found what was causing the error.

must write:
if not (TADOQuery(Form1.FindComponent('QAgenda' + inttostr(ct))).isEmpty) then

insteed of:
if not (TADOQuery(FindComponent('Form1.QAgenda' + inttostr(ct))).isEmpty) then

Thanks again for your help

shaneholmes

Yeah, but if you place all the tables on a TDatamodule, then you wont have to deal with

the different forms

if Form1.QAgenda1.IsEmpty then
...
if Form2.QAgenda1.IsEmpty then
...
if Form3.QAgenda1.IsEmpty then
...
if Form4.QAgenda1.IsEmpty then
...
if Form5.QAgenda1.IsEmpty then
...
if Form6.QAgenda1.IsEmpty then
...
if Form7.QAgenda1.IsEmpty then

they will all be centralized on one form

SMILE

Shane