Custom model for QTreeView with SQLite data source

Hello,

I'm getting strange qDebug behaviour. Here is the code:

Code:

---

// TreeModel.hpp
#ifndef TREEMODEL_HPP
#define TREEMODEL_HPP
 
#include <QAbstractItemModel>
 
class TreeModel : public QAbstractItemModel
{
    Q_OBJECT
 
public:
    explicit TreeModel(QObject *parent = 0);
    int rowCount(const QModelIndex &parent = QModelIndex()) const;
    int columnCount(const QModelIndex &parent = QModelIndex()) const;
    QVariant data(const QModelIndex &item, int role) const;
    QVariant headerData(int section, Qt::Orientation orientation, int role = Qt::DisplayRole) const;
    Qt::ItemFlags flags(const QModelIndex &index) const;
    QModelIndex index(int row, int column, const QModelIndex &parent = QModelIndex()) const;
    QModelIndex parent(const QModelIndex &index) const;
 
};
 
#endif // TREEMODEL_HPP

---

Code:

---

// TreeModel.cpp
#include <QSqlQuery>
#include <QSqlError>
#include <QVector>
#include <QMessageBox>
 
#include "TreeModel.hpp"
 
TreeModel::TreeModel(QObject *parent) :
    QAbstractItemModel(parent)
{
}
 
int TreeModel::rowCount(const QModelIndex &parent) const
{
    // top level items
    if(!parent.isValid())
    {
        QSqlQuery q1("SELECT id FROM table_a");
 
        // QSQLITE doesn't support size() function
        int size = 0;
        while(q1.next())
            size++;
 
        return size;
    }
 
    // children
    if(parent.internalId() == 0)
    {
        QSqlQuery q2;
        q2.prepare("SELECT id FROM table_b WHERE table_a_id = :table_a_id");
        q2.bindValue(":table_a_id", parent.data().toInt());
        q2.exec();
 
        // QSQLITE doesn't support size() function
        int size = 0;
        while(q2.next())
            size++;
 
        return size;
    }
 
    return 0;
}
 
int TreeModel::columnCount(const QModelIndex &parent) const
{
    Q_UNUSED(parent);
 
    return 1;
}
 
 
QVariant TreeModel::data(const QModelIndex &item, int role) const
{
    if(!item.isValid())
        return QVariant();
 
    if(role == Qt::DisplayRole)
    {
        if(item.internalId() == 0)
        {
            // top level item...
 
            if(item.column() == 0)
            {
                QSqlQuery q1("SELECT id FROM table_a ORDER BY id");
 
                // QSQLITE doesn't like seek() function
                int r = 0;
                while(q1.next())
                {
                    if(r == item.row())
                        return q1.value(0).toInt();
                    r++;
                }
            }
        }
        else
        {
            // child...
 
            QSqlQuery q2;
            q2.prepare("SELECT id FROM table_b WHERE table_a_id = :table_a_id ORDER BY id");
            q2.bindValue(":table_a_id", item.parent().data().toInt());
            q2.exec();
 
            // QSQLITE doesn't like seek() function
            int r = 0;
            while(q2.next())
            {
                if(r == item.row())
                    return q2.value(0).toInt();
                r++;
            }
        }
    }
 
    return QVariant();
}
 
 
QVariant TreeModel::headerData(int section, Qt::Orientation orientation, int role) const
{
    if(orientation == Qt::Horizontal && role == Qt::DisplayRole && section == 0)
        return QString("Id");
 
    return QVariant();
}
 
 
Qt::ItemFlags TreeModel::flags(const QModelIndex &index) const
{
    Q_UNUSED(index);
 
    return Qt::ItemIsEnabled | Qt::ItemIsSelectable;
}
 
 
QModelIndex TreeModel::index(int row, int column, const QModelIndex &parent) const
{
    if(!parent.isValid())
        return createIndex(row, column, 0);
 
    return createIndex(row, column, 1);
}
 
 
QModelIndex TreeModel::parent(const QModelIndex &index) const
{
    if(index.isValid())
    {
        if(index.internalId() == 0)
            return QModelIndex();
        else
        {
            // this line is fine
            qDebug("internalId != 0");
 
            // this line is missing...
            qDebug("data: %i", index.data().toInt());
 
            /*
 
             return valid QModelIndex...
 
             */
        }
    }
 
    return QModelIndex();
}

---

Line 143 in TreeModel.cpp doesn't print any output. I was working on parent() function and I discovered that something is wrong with index.data(). I've added qDebug() and... surprise! - qDebug() gives no output. What am I missing here?