First login attempt works if it's correct, but if it's incorrect then other correct attemp-CodePudding

void __fastcall TFormLogin::btnLoginClick(TObject *Sender)
{
    UnicodeString query = "select * from admin where korisnickoIme = '"   editKorisnicko->Text  
                     "' AND lozinka = '"   editLozinka->Text   "'";
    AnsiString ansiQuery = query;

    ADOQuery1->ConnectionString = "Provider=SQLOLEDB.1;Integrated Security=SSPI;Persist Security Info=False;Initial Catalog=KnjiznicaManagement;Data Source=KUKICRO\\SQLEXPRESS;Use Procedure for Prepare=1;Auto Translate=True;Packet Size=4096;Workstation ID=KUKICRO;Use Encryption for Data=False;Tag with column collation when possible=False";
    ADOQuery1->SQL->Add(ansiQuery);

    ADOQuery1->Prepared = true;

    try
    {
        ADOQuery1->Active = true;
    }
    catch (EADOError& e)
    {
        MessageDlg("Error spajanja", mtError,
                      TMsgDlgButtons() << mbOK, 0);
        return;
    }

    TDataSource* Src = new TDataSource(this);
    Src->DataSet = ADOQuery1;
    Src->Enabled = true;

    if(Src->DataSet->RecordCount < 1){
        labelPrijava->Visible = true;
        ADOQuery1->Prepared = false;

        Src->Enabled = false;

        try{
            ADOQuery1->Active = false;
        }
        catch (EADOError& e){
            MessageDlg("Error odspajanja", mtError,
                  TMsgDlgButtons() << mbOK, 0);
        }
        return;
    }

    FormMain->labelUlogiran->Caption = Src->DataSet->FieldByName("korisnickoIme")->AsString;
    FormLogin->Close();
}

Code from above is my OnClick button event code. It should simulate login from a database table "admin" that contains "korisnickoIme" in the username field and "lozinka" in the password field. When I type in the correct username and password, the first attempt works, but if I type in the wrong username and password and then the correct one, it doesn't work. When I go through with the debugger, the last if is true but it shouldn't be.

CodePudding user response：

This line:

ADOQuery1->SQL->Add(ansiQuery);

adds the ansiQuery to the end of the SQL collection for ADOQuery. When you click the button a second time, the new query is added to the end, but the original incorrect query is still at the start of the collection, so it is run first.

Solution: Clear out the collection on each button click. Add the following before the Add line:

ADOQuery1->SQL->Clear()