Setup a Firedac fdquery and fdconnection in runtime

Question

I need to setup/run a fdconnection and fdquery, in runtime. But how?

I am trying this in my code:

var
 LocalConnection: TFDConnection;
 LicencasTable: TFDQuery;
 FDPhysMySQLDriverLink1: TFDPhysMySQLDriverLink;
 FDGUIxWaitCursor1: TFDGUIxWaitCursor;
 oParams: TStrings;
begin

  LocalConnection := TFDConnection.Create(Self);

  FDPhysMySQLDriverLink1 := TFDPhysMySQLDriverLink.Create(Self);
  FDGUIxWaitCursor1      := TFDGUIxWaitCursor.Create(Self);
  FDPhysMySQLDriverLink1.VendorLib := ExtractFilePath(Application.exename)+'libmysql.dll';


  try
   if Variaveis.hostbd <> '' then begin
    oParams := TStringList.Create;
    oParams.Add('Server=' + Variaveis.hostbd);
    oParams.Add('Database='+Variaveis.databasebd);
    oParams.Add('User_Name='+Variaveis.usuariobd);
    oParams.Add('Password='+Variaveis.password);
    oParams.Add('DriverID=MySQL');
    LocalConnection.Params.UserName := Variaveis.usuariobd;
    LocalConnection.Params.Password := Variaveis.password;
    FDManager.AddConnectionDef('bloqueio', 'MySQL', oParams);
    LocalConnection.DriverName := 'MySQL';
    LocalConnection.LoginPrompt := false;
    LocalConnection.Connected := true;
    if LocalConnection.Connected then
        // Busca o registro do sistema no bd
        LicencasTable := TFDQuery.Create(Self);
        LicencasTable.Connection :=  LocalConnection;
        ShowMessage(Pchar(LicencasTable.Connection));
        LicencasTable.Close;
        LicencasTable.SQL.Clear;
        ShowMessage('Before open');
        LicencasTable.Open('select * from licencas');
        ShowMessage('After open');
        LicencasTable.Active := true;
        if LicencasTable.Active  then begin
          ShowMessage('Active');
        end;
        if not LicencasTable.Active  then begin
          ShowMessage('This is not Active');
        end;
   end;
  except
    oParams.Free;
  end;

Everything works correctly, until reach the "LicencasTable.Open('select * from licencas');"

The query.open simply dont works, and gives me no error too. Why not open, and not show me a error?

What am I forgetting to do?

Answer 1

Your code is incorrect in a couple of ways. First, you don't have to close it or clear the SQL on a newly created query. Second, you don't typically use the Open method to set up the SQL statement. Third, you're using a try..except to free resources, which is incorrect; if no exception occurs, you have a memory leak. You should be using a try..finally instead.

 try
   if Variaveis.hostbd <> '' then begin
    oParams := TStringList.Create;
    oParams.Add('Server=' + Variaveis.hostbd);
    oParams.Add('Database='+Variaveis.databasebd);
    oParams.Add('User_Name='+Variaveis.usuariobd);
    oParams.Add('Password='+Variaveis.password);
    oParams.Add('DriverID=MySQL');
    LocalConnection.Params.UserName := Variaveis.usuariobd;
    LocalConnection.Params.Password := Variaveis.password;
    FDManager.AddConnectionDef('bloqueio', 'MySQL', oParams);
    LocalConnection.DriverName := 'MySQL';
    LocalConnection.LoginPrompt := false;
    LocalConnection.Connected := true;
    if LocalConnection.Connected then
    begin
        // Busca o registro do sistema no bd
        LicencasTable := TFDQuery.Create(Self);
        LicencasTable.Connection :=  LocalConnection;
        ShowMessage(Pchar(LicencasTable.Connection));
        ShowMessage('Before open');
        LicencasTable.SQL.Text := 'select * from licencas';
        LicencasTable.Active := true;
        if LicencasTable.Active  then begin
          ShowMessage('Active');
        end;
        if not LicencasTable.Active  then begin
          ShowMessage('This is not Active');
        end;
    end;
  finally
    oParams.Free;
  end;