How me get acces ui from another class?

Question

I have a database in a separate widget class datbase.ui that I insert as tab in mainwindow.ui. I want that when initializing the connection in the class datbase.ui statusbar in mainwindow.ui to change depending.

datbase.cpp

void DatBase::on_pushButton_clicked()
{
    QSqlDatabase ddbb = QSqlDatabase::addDatabase("QSQLITE");
    ddbb.setDatabaseName(".../db/ddberdbsqlite");
    if (ddbb.open()){
        // It is necessary that this status is displayed in mainwindow.ui
        // How to get access to gui mainwindow?
        ui->statusBar->showMessage("Successful connection!");
    }
    else{
        ui->statusBar->showMessage("Not Successful connection!");
    }
}

mainwindow.cpp

#include "mainwindow.h"
#include "ui_mainwindow.h"
#include "datbase.h"

MainWindow::MainWindow(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::MainWindow)
{
    ui->setupUi(this);
    setWindowTitle("Measurement DDEBR");
    connect(ui->tabWidget, QTabWidget::currentChanged, this,  MainWindow::showTabPageIndex);
    DatBase *tabDatBase = new DatBase();
    ui->tabWidget->insertTab(0, tabDatBase, "Data Base");
}

MainWindow::~MainWindow()
{
    delete ui;
}