Problems querying on PostgreSQl

[jreromero]

Dialog_Login.h*******

#include <QDialog>
#include <QtSql>
#include <QSqlDatabase>
 
class Dialog_Login;
}
 
class Dialog_Login : public QDialog
{
Q_OBJECT
 
public:
explicit Dialog_Login(QWidget *parent = 0);
~Dialog_Login();
 
void Rellenar_Usuarios();
QSqlQueryModel *Modelo1;
QSqlDatabase db;
}:

#include <QDialog>
#include <QtSql>
#include <QSqlDatabase>

class Dialog_Login;
}

class Dialog_Login : public QDialog
{
Q_OBJECT

public:
explicit Dialog_Login(QWidget *parent = 0);
~Dialog_Login();

void Rellenar_Usuarios();
QSqlQueryModel *Modelo1;
QSqlDatabase db;
}:

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Dialog_Login.cpp*

void Dialog_Login::Rellenar_Usuarios()
{
 
db = QSqlDatabase::addDatabase("QPSQL");
db.setDatabaseName("*******");
db.setHostName("********");
db.setUserName("*****");
db.setPassword("*****");
db.setPort(5432);
 
 
 
 
 
if(db.open())
 
{
    QSqlQuery query;
 
 
 
      query.exec("SELECT id_usuario FROM Usuario");
 
      ui->tableWidget->setRowCount(1);
 
                 ui->tableWidget->setColumnCount(1);
                 ui->tableWidget->setSizePolicy(QSizePolicy::Expanding,QSizePolicy::Expanding);
 
 
                 ui->tableWidget->setHorizontalHeaderLabels(QString("Usuarios").split(";"));
 
             int i=0;
             while (query.next()) {
 
 
               ui->tableWidget->setItem(i,0,new QTableWidgetItem(query.value(1).toString()));
 
 
                  i++;
             ui->tableWidget->insertRow(i);
 
}
}
}
 
void Dialog_Login::on_pushButton_2_clicked()
{
Rellenar_Usuarios();
}

void Dialog_Login::Rellenar_Usuarios()
{

db = QSqlDatabase::addDatabase("QPSQL");
db.setDatabaseName("*******");
db.setHostName("********");
db.setUserName("*****");
db.setPassword("*****");
db.setPort(5432);





if(db.open())

{
    QSqlQuery query;



      query.exec("SELECT id_usuario FROM Usuario");

      ui->tableWidget->setRowCount(1);

                 ui->tableWidget->setColumnCount(1);
                 ui->tableWidget->setSizePolicy(QSizePolicy::Expanding,QSizePolicy::Expanding);


                 ui->tableWidget->setHorizontalHeaderLabels(QString("Usuarios").split(";"));

             int i=0;
             while (query.next()) {


               ui->tableWidget->setItem(i,0,new QTableWidgetItem(query.value(1).toString()));


                  i++;
             ui->tableWidget->insertRow(i);

}
}
}

void Dialog_Login::on_pushButton_2_clicked()
{
Rellenar_Usuarios();
}

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I need to see what is in the "id_usuario" field in the user table on in QTableWidget, only for testing
But when i running it, the QTableWidget doesn't fill! What's wrong?? I'm Sorry my bad English!! Thanks