Chapter 2: bookdelegate.cpp to bookdelegate.py

Now that your database is in place, port the C++ code for the BookDelegate class. This class offers a delegate to present and edit the data in a QTableView. It inherits QSqlRelationalDelegate interface, which offers features specific for handling relational databases, such as a combobox editor for foreign key fields. To begin with, create bookdelegate.py and add the following imports to it:

1from __future__ import annotations
2
3import copy
4import os
5from pathlib import Path
6
7from PySide6.QtSql import QSqlRelationalDelegate
8from PySide6.QtWidgets import (QItemDelegate, QSpinBox, QStyledItemDelegate,

After the necessary import statements, port the constructor code for the BookDelegate class. Both the C++ and Python versions of this code initialize a QSqlRelationalDelegate and QPixmap instance. Here is how they look:

C++ version

1        QStyleOptionViewItem opt = option;
2        // Since we draw the grid ourselves:
3        opt.rect.adjust(0, 0, -1, -1);
4        QSqlRelationalDelegate::paint(painter, opt, index);
5    } else {
6        const QAbstractItemModel *model = index.model();

Python version

1from PySide6.QtWidgets import (QItemDelegate, QSpinBox, QStyledItemDelegate,
2    QStyle, QStyleOptionViewItem)
3from PySide6.QtGui import QMouseEvent, QPixmap, QPalette, QImage
4from PySide6.QtCore import QEvent, QSize, Qt, QUrl
5
6
7class BookDelegate(QSqlRelationalDelegate):
8    """Books delegate to rate the books"""

Note

The Python version loads the QPixmap using the absolute path of star.png in the local filesystem.

As the default functionality offered by the QSqlRelationalDelegate is not enough to present the books data, you must reimplement a few functions. For example, painting stars to represent the rating for each book in the table. Here is how the reimplemented code looks like:

C++ version (bookdelegate)

 1        const QAbstractItemModel *model = index.model();
 2        QPalette::ColorGroup cg = (option.state & QStyle::State_Enabled) ?
 3            (option.state & QStyle::State_Active) ?
 4                        QPalette::Normal :
 5                        QPalette::Inactive :
 6                        QPalette::Disabled;
 7
 8        if (option.state & QStyle::State_Selected)
 9            painter->fillRect(
10                        option.rect,
11                        option.palette.color(cg, QPalette::Highlight));
12
13        int rating = model->data(index, Qt::DisplayRole).toInt();
14        int width = star.width();
15        int height = star.height();
16        int x = option.rect.x();
17        int y = option.rect.y() + (option.rect.height() / 2) - (height / 2);
18        for (int i = 0; i < rating; ++i) {
19            painter->drawPixmap(x, y, star);
20            x += width;
21        }
22        // Since we draw the grid ourselves:
23        drawFocus(painter, option, option.rect.adjusted(0, 0, -1, -1));
24    }
25
26    QPen pen = painter->pen();
27    painter->setPen(option.palette.color(QPalette::Mid));
28    painter->drawLine(option.rect.bottomLeft(), option.rect.bottomRight());
29    painter->drawLine(option.rect.topRight(), option.rect.bottomRight());
30    painter->setPen(pen);
31}
32
33QSize BookDelegate::sizeHint(const QStyleOptionViewItem &option,
34                                 const QModelIndex &index) const
35{
36    if (index.column() == 5)
37        return QSize(5 * star.width(), star.height()) + QSize(1, 1);
38    // Since we draw the grid ourselves:
39    return QSqlRelationalDelegate::sizeHint(option, index) + QSize(1, 1);
40}
41
42bool BookDelegate::editorEvent(QEvent *event, QAbstractItemModel *model,
43                               const QStyleOptionViewItem &option,
44                               const QModelIndex &index)
45{
46    if (index.column() != 5)
47        return QSqlRelationalDelegate::editorEvent(event, model, option, index);
48
49    if (event->type() == QEvent::MouseButtonPress) {
50        QMouseEvent *mouseEvent = static_cast<QMouseEvent*>(event);
51        int stars = qBound(0, int(0.7 + qreal(mouseEvent->pos().x()
52            - option.rect.x()) / star.width()), 5);
53        model->setData(index, QVariant(stars));
54        // So that the selection can change:
55        return false;
56    }
57
58    return true;
59}
60
61QWidget *BookDelegate::createEditor(QWidget *parent,
62                                    const QStyleOptionViewItem &option,
63                                    const QModelIndex &index) const
64{
65    if (index.column() != 4)
66        return QSqlRelationalDelegate::createEditor(parent, option, index);
67
68    // For editing the year, return a spinbox with a range from -1000 to 2100.
69    QSpinBox *sb = new QSpinBox(parent);
70    sb->setFrame(false);
71    sb->setMaximum(2100);
72    sb->setMinimum(-1000);
73
74    return sb;
75}

Python version (bookdelegate)

 1
 2    def __init__(self, parent=None):
 3        QSqlRelationalDelegate.__init__(self, parent)
 4        star_png = Path(__file__).parent / "images" / "star.png"
 5        self.star = QPixmap(star_png)
 6
 7    def paint(self, painter, option, index):
 8        """ Paint the items in the table.
 9
10            If the item referred to by <index> is a StarRating, we
11            handle the painting ourselves. For the other items, we
12            let the base class handle the painting as usual.
13
14            In a polished application, we'd use a better check than
15            the column number to find out if we needed to paint the
16            stars, but it works for the purposes of this example.
17        """
18        if index.column() != 5:
19            # Since we draw the grid ourselves:
20            opt = copy.copy(option)
21            opt.rect = option.rect.adjusted(0, 0, -1, -1)
22            QSqlRelationalDelegate.paint(self, painter, opt, index)
23        else:
24            model = index.model()
25            if option.state & QStyle.State_Enabled:
26                if option.state & QStyle.State_Active:
27                    color_group = QPalette.Normal
28                else:
29                    color_group = QPalette.Inactive
30            else:
31                color_group = QPalette.Disabled
32
33            if option.state & QStyle.State_Selected:
34                painter.fillRect(option.rect,
35                    option.palette.color(color_group, QPalette.Highlight))
36            rating = model.data(index, Qt.DisplayRole)
37            width = self.star.width()
38            height = self.star.height()
39            x = option.rect.x()
40            y = option.rect.y() + (option.rect.height() / 2) - (height / 2)
41            for i in range(rating):
42                painter.drawPixmap(x, y, self.star)
43                x += width
44
45            # Since we draw the grid ourselves:
46            self.drawFocus(painter, option, option.rect.adjusted(0, 0, -1, -1))
47
48        pen = painter.pen()
49        painter.setPen(option.palette.color(QPalette.Mid))
50        painter.drawLine(option.rect.bottomLeft(), option.rect.bottomRight())
51        painter.drawLine(option.rect.topRight(), option.rect.bottomRight())
52        painter.setPen(pen)
53
54    def sizeHint(self, option, index):
55        """ Returns the size needed to display the item in a QSize object. """
56        if index.column() == 5:
57            size_hint = QSize(5 * self.star.width(), self.star.height()) + QSize(1, 1)
58            return size_hint
59        # Since we draw the grid ourselves:
60        return QSqlRelationalDelegate.sizeHint(self, option, index) + QSize(1, 1)
61
62    def editorEvent(self, event, model, option, index):
63        if index.column() != 5:
64            return False
65
66        if event.type() == QEvent.MouseButtonPress:
67            mouse_pos = event.pos()
68            new_stars = int(0.7 + (mouse_pos.x() - option.rect.x()) / self.star.width())
69            stars = max(0, min(new_stars, 5))
70            model.setData(index, stars)
71            # So that the selection can change
72            return False
73
74        return True
75
76    def createEditor(self, parent, option, index):
77        if index.column() != 4:
78            return QSqlRelationalDelegate.createEditor(self, parent, option, index)
79
80        # For editing the year, return a spinbox with a range from -1000 to 2100.
81        spinbox = QSpinBox(parent)
82        spinbox.setFrame(False)
83        spinbox.setMaximum(2100)
84        spinbox.setMinimum(-1000)
85        return spinbox

Now that the delegate is in place, run the following main.py to see how the data is presented:

 1from __future__ import annotations
 2
 3import sys
 4
 5from PySide6.QtCore import Qt
 6from PySide6.QtSql import QSqlQueryModel
 7from PySide6.QtWidgets import QTableView, QApplication
 8
 9import createdb
10from bookdelegate import BookDelegate
11
12if __name__ == "__main__":
13    app = QApplication()
14    createdb.init_db()
15
16    model = QSqlQueryModel()
17    model.setQuery("select title, author, genre, year, rating from books")
18
19    table = QTableView()
20    table.setModel(model)
21    table.setItemDelegate(BookDelegate())
22    table.resize(800, 600)
23    table.show()
24
25    sys.exit(app.exec())

Here is how the application will look when you run it:

Books table data

The only difference you’ll notice now in comparison to chapter 1 is that the rating column looks different.

Try improving the table even further by adding these features:

  • Title for each column

  • SQL relation for the author_id and genre_id columns

  • Set a title to the window

With these features, this is how your table will look like:

Books table with SQL relation