How do i use SQL codeing Within my class?

Question

I have created a class that has to use SQL-code to do a validation check from my database but when i try to run my program it does not use the ADOquery from my form. I have tried to fix it by adding my main unit to my class's unit but it then gives a circulation error. I have also tried to add Form1 into the uses(that is the name of my form and i only have one form) but then it does not understand Form1. If any one can help, it would be very appreciated.

orait this is in my class:

procedure TCheckA.CheckIfAdmin;
var iRecordA : Integer;
begin
    qryInfo.Active := False;
    qryInfo.SQL.Clear;
    qryInfo.SQL.Add(' Select [Lid Naam], [Lid Wagwoord], Adminustrateur ');
    qryInfo.SQL.Add(' From [CATSA Lede] ');
    qryInfo.SQL.Add(' Where [Lid Naam] = "'+fgebruikernaam+'"and [Lid Wagwoord] = "'+fpassword+'" and Adminustrateur = True ');
    qryInfo.Active := True;
    iRecordA := qryinfo.recordcount;


 if iRecordA = 1
  then begin
   fAdminAnswer := True;
   end
  else begin
   fAdminAnswer := False;
  end;
end;

Then it throughs this error: [Error] IntekenCheck.pas(29): Undeclared identifier: 'qryInfo'

Then if i try to put my main unit in my class's unit Like:

unit IntekenCheck;

interface
 uses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs, ComCtrls, StdCtrls, Buttons, jpeg, ExtCtrls, XPMan, Grids,
  DBGrids, DB, ADODB, Math, AdminCheck, Chairmin_u{main unit};

Then the error is: [Fatal Error] IntekenCheck.pas(7): Circular unit reference to 'IntekenCheck'

Can you show the code that's failing and provide specific error messages that you receive? — David
– David, Commented Sep 17, 2013 at 18:24
Hay guys when i posted this question I was still programming stupid and did not think to build my queries in my classes and then just return it to my main program. Thank you all for help i do appreciate it and i will keep these tips in mind. BTW i now code in C# rather then delphi but principles stay the same. — Johann Nel
– Johann Nel, Commented Nov 1, 2015 at 1:41

Ken White · Accepted Answer · 2013-09-17 20:02:11Z

1

Pass the query into your class, and use it there:

procedure TCheckA.CheckIfAdmin(const Query: TAdoQuery);
begin
  AQuery.Active := False;
  AQuery.SQL.Clear;
  AQuery.SQL.Add(' Select [Lid Naam], [Lid Wagwoord], Adminustrateur ');
  AQuery.SQL.Add(' From [CATSA Lede] ');
  AQuery.SQL.Add(' Where [Lid Naam] = "' + fgebruikernaam +
                 '"and [Lid Wagwoord] = "'+ fpassword + 
                 '" and Adminustrateur = True ');
  AQuery.Active := True;
  fAdminAnswer := (AQuery.RecordCount = 1);
end;

(You should also change to use parameterized queries instead rather than contatenation with +. It's much more secure. There are many other questions here relating to parameterized queries and Delphi; a quick search on [delphi] parameter query should find them for you.)

answered Sep 17, 2013 at 20:02

Ken White

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