QTableView inside QTabWidget does not show data

Question

I have a QTabWidget, each tab contains a QTableView. The tableviews use QTableModels which reads data from an sqlite database.

The models are kept as member variables, so I don't think it's a scope problem (which is the most frequent problem I've found by searching for the issue).

Other db operations works: I tried populating / creating tables in the code, and those operation are correctly executed.

The following is the class definition:

#include <QMainWindow>
#include <QtSql>
#include <QString>

namespace Ui {
    class MainWindow;
}

class AlisnagMainWindow : public QMainWindow
{
    Q_OBJECT

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

protected:
    bool createDB(const QString& filename);
    bool loadDB(const QString& filename);

protected slots:
    void newFile();
    void openFile();
    void addRow();

private:
    void initModels();
    Ui::MainWindow *ui;
    QSqlDatabase db;
    QSqlRelationalTableModel    *loans_model;
    QSqlTableModel              *people_model;
    QSqlRelationalTableModel    *items_model;
};

This is the constructor:

AlisnagMainWindow::AlisnagMainWindow(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::MainWindow),
    loans_model( new QSqlRelationalTableModel(this) ),
    people_model( new QSqlTableModel(this) ),
    items_model( new QSqlRelationalTableModel(this) )
{
    ui->setupUi(this);

    db = QSqlDatabase::addDatabase("QSQLITE");

    connect(ui->actionNew,  SIGNAL(triggered()), this, SLOT(newFile()));
    connect(ui->actionOpen, SIGNAL(triggered()), this, SLOT(openFile()));
}

This is how I initialized the models and the views:

void AlisnagMainWindow::initModels(){
    people_model->setTable("people");
    people_model->setEditStrategy(QSqlTableModel::OnRowChange);
    people_model->select();
    people_model->setHeaderData(0, Qt::Horizontal, tr("Name"));
    people_model->setHeaderData(1, Qt::Horizontal, tr("Surname"));
    people_model->setHeaderData(2, Qt::Horizontal, tr("Phone"));
    people_model->setHeaderData(3, Qt::Horizontal, tr("Address"));

    items_model->setTable("items");
    items_model->setEditStrategy(QSqlTableModel::OnRowChange);
    items_model->setRelation(3, QSqlRelation("categories","id","name"));
    items_model->select();

    loans_model->setTable("loans");
    loans_model->setEditStrategy(QSqlTableModel::OnRowChange);
    loans_model->setRelation(0, QSqlRelation("items","id","name"));
    loans_model->setRelation(1, QSqlRelation("people","id","name"));
    loans_model->select();

    ui->peopleView->setModel(people_model);
    ui->peopleView->hideColumn(0);

    ui->itemsView->setModel(items_model);
    ui->itemsView->hideColumn(0);

    ui->loansView->setModel(loans_model);
    ui->loansView->hideColumn(0);

}

The database is loaded as follows:

bool AlisnagMainWindow::loadDB(const QString &filename)
{
    if(db.isOpen())
        db.close();
    db.setDatabaseName(filename);

    if( !db.open() ){
        QMessageBox::critical(this, tr("Error"),
                              tr("Could not open db %1").arg(filename),
                              QMessageBox::Ok);
        return false;
    }

    ui->statusBar->showMessage("DB successfully opened!");
    return true;

}

Then this is how is all combined:

void AlisnagMainWindow::openFile()
{
    QString filename = QFileDialog::getOpenFileName(this, tr("Choose DB file"),
                                                    ".", "*.db");
    loadDB(filename);

    initModels();
}

The file I'm opening has been populated externally. When I run the code, neither the data nor the headers are shown. Any insight?

Thanks in advance.

EDIT: Added some context as requested

Answer 1

As Greenflow pointed out, problem was in the constructor, in particular in the order of initialization.
The constructor is modified as follows

AlisnagMainWindow::AlisnagMainWindow(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::MainWindow),
    db ( QSqlDatabase::addDatabase("QSQLITE")),
    loans_model( new QSqlRelationalTableModel(this, db) ),
    people_model( new QSqlTableModel(this, db) ),
    items_model( new QSqlRelationalTableModel(this, db) )
{
    ui->setupUi(this);
    connect(ui->actionNew,  SIGNAL(triggered()), this, SLOT(newFile()));
    connect(ui->actionOpen, SIGNAL(triggered()), this, SLOT(openFile()));
}