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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:
.. literalinclude:: bookdelegate.py
:language: python
:linenos:
:lines: 3-10
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
-------------
.. literalinclude:: bookdelegate.cpp
:language: c++
:linenos:
:lines: 17-22
Python version
---------------
.. literalinclude:: bookdelegate.py
:language: python
:linenos:
:lines: 10-17
.. 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)
--------------------------
.. literalinclude:: bookdelegate.cpp
:language: c++
:linenos:
:lines: 22-
Python version (bookdelegate)
-----------------------------
.. literalinclude:: bookdelegate.py
:language: python
:linenos:
:lines: 18-
Now that the delegate is in place, run the following
``main.py`` to see how the data is presented:
.. literalinclude:: main.py
:language: python
:linenos:
:lines: 3-
Here is how the application will look when you run it:
.. image:: images/chapter2_books.png
:alt: Books table data
The only difference you'll notice now in comparison to
:doc:`chapter 1 <../chapter1/chapter1>` 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:
.. image:: images/chapter2_books_with_relation.png
:alt: Books table with SQL relation
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