Using parameters with ADO Query (mysql/MyConnector)

Question

Today I downloaded and installed MyConnector so I can use Mysql with ADO, everything installed, OK!, I can make connection with ODBC and do a connection from my delphi environment.

when I build my Query at runetime, I get an error saying :

---------------------------
Debugger Exception Notification
---------------------------
Project Project1.exe raised exception class EOleException with message 'Arguments are of the wrong type, are out of acceptable range, or are in conflict with one another'. Process stopped. Use Step or Run to continue.
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OK   Help   
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function TForm1.CreateSQL : TADOQuery;
begin
  result := TADOQuery.create(self);
  with Result do
  begin
    Connection     := MainConnection;
    CursorLocation := clUseServer;
    CursorType     := ctStatic;
    CacheSize      := 50;
    AutoCalcFields := true;
    ParamCheck     := true;
    Prepared       := true;
  end;
end;

procedure TForm1.login();
begin
  with CreateSQL do
  try
    with SQL do
    begin
      add('SELECT                       ');
      add('  *                          ');
      add('FROM                         ');
      add('  LisenswebUsers             ');
      add('WHERE                        ');
      add('  UserName     = :MyUsername '); // debugger exception here
      add('AND                          ');
      add('  UserPassword = :MyPassword '); // debugger exception here
      with Parameters do
      begin
        ParamByName('MyUsername').value := txtLogin.text;
        ParamByName('MyPassword').value := strmd5(txtPassword.text);
      end;
      Open;

      if Recordcount <> 1 then
      begin
        lblLoggedinAs.Text := format('Du er logget inn som: %s (%s)',[FieldByName('Username').AsString,FieldByName('UserEmailaddress').AsString]);
        MainPageControl.ActivePageIndex := 1;
      end else
      begin
        txtPassword.Text := '';
        txtPassword.SetFocus;
      end;
    end;
  finally
   free;
  end;
end;

The strangest thing is that this works if I turn off debugging in delphi.

Answer 1

I would try adding SQL.BeginUpdate/SQL.EndUpdate around the Adds, otherwise the SQL text will be parsed every time you call "Add".

This is generally a good idea, as ADOQuery.SQL is a TStringList that has an OnChange event that sets the CommandText. SetCommandText text then end up calling TADOCommand.AssignCommandText which does a fair amount of work parsing params, and setting CommandObject.CommandText. Sometimes drivers will fail with partial SQL statements, but this stuff looks OK.

I had a similar problem many years ago - that's why I learnt about this stuff!

procedure TForm1.login();
var
  Qry : TADOQuery;
begin
  Qry := CreateSQL;
  try
    Qry.SQL.BeginUpdate;

    Qry.SQL.Add('SELECT');
    Qry.SQL.Add('  *');
    Qry.SQL.Add('FROM');
    Qry.SQL.Add('  LisenswebUsers');
    Qry.SQL.Add('WHERE UserName = :MyUsername '); // debugger exception here
    Qry.SQL.Add('  AND UserPassword = :MyPassword '); // debugger exception here

    Qry.SQL.EndUpdate;
    Qry.Parameters.ParamByName('MyUsername').value := txtLogin.text;
    Qry.Parameters.ParamByName('MyPassword').value := strmd5(txtPassword.text);
    Qry.Open;

    if Qry.Recordcount <> 1 then
    begin
      lblLoggedinAs.Text := format('Du er logget inn som: %s (%s)',[FieldByName('Username').AsString,FieldByName('UserEmailaddress').AsString]);
      MainPageControl.ActivePageIndex := 1;
    end
    else
    begin
      txtPassword.Text := '';
      txtPassword.SetFocus;
    end;
  finally
    Qry.Free;
  end;
end;

BTW, the nested withs are really ugly (let the holy war begin)

I will sometimes use with, but would never nest three levels! If you are, at least reduce the scope of with SQL so it ends before with Parameters.

Answer 2

Try setting an explicit datatype :

CreateSql.Parameters.ParamByName('MyUserName').DataType := ftString;