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=========================
Defining the Domain Model
=========================
The first change we'll make to our stock ``pcreate``-generated application will
be to define a :term:`domain model` constructor representing a wiki page.
We'll do this inside our ``models.py`` file.
Making Edits to ``models.py``
-----------------------------
.. note::
There is nothing special about the filename ``models.py``. A
project may have many models throughout its codebase in arbitrarily-named
files. Files implementing models often have ``model`` in their filenames
(or they may live in a Python subpackage of your application package named
``models``) , but this is only by convention.
Open ``tutorial/tutorial/models.py`` file and edit it to look like the
following:
.. literalinclude:: src/models/tutorial/models.py
:linenos:
:language: py
:emphasize-lines: 20-22,25
(The highlighted lines are the ones that need to be changed.)
The first thing we've done is remove the stock ``MyModel`` class
from the generated ``models.py`` file. The ``MyModel`` class is only a
sample and we're not going to use it.
Then, we added a ``Page`` class. Because this is a SQLAlchemy application,
this class inherits from an instance of
:func:`sqlalchemy.ext.declarative.declarative_base`.
.. literalinclude:: src/models/tutorial/models.py
:pyobject: Page
:linenos:
:language: python
As you can see, our ``Page`` class has a class level attribute
``__tablename__`` which equals the string ``'pages'``. This means that
SQLAlchemy will store our wiki data in a SQL table named ``pages``. Our
``Page`` class will also have class-level attributes named ``id``, ``name`` and
``data`` (all instances of :class:`sqlalchemy.schema.Column`).
These will map to columns in the ``pages`` table.
The ``id`` attribute will be the primary key in the table.
The ``name`` attribute will be a text attribute, each value of
which needs to be unique within the column. The ``data`` attribute is a text
attribute that will hold the body of each page.
Changing ``scripts/initializedb.py``
------------------------------------
We haven't looked at the details of this file yet, but within the ``scripts``
directory of your ``tutorial`` package is a file named ``initializedb.py``. Code
in this file is executed whenever we run the ``initialize_tutorial_db`` command
(as we did in the installation step of this tutorial).
Since we've changed our model, we need to make changes to our ``initializedb.py``
script. In particular, we'll replace our import of ``MyModel`` with one of
``Page`` and we'll change the very end of the script to create a ``Page``
rather than a ``MyModel`` and add it to our ``DBSession``.
Open ``tutorial/tutorial/scripts/initializedb.py`` and edit it to look like the
following:
.. literalinclude:: src/models/tutorial/scripts/initializedb.py
:linenos:
:language: python
:emphasize-lines: 14,36
(Only the highlighted lines need to be changed.)
Installing the Project and re-initializing the Database
-------------------------------------------------------
Because our model has changed, in order to reinitialize the database, we need
to rerun the ``initialize_tutorial_db`` command to pick up the changes you've made
to both the models.py file and to the initializedb.py file.
See :ref:`initialize_db_wiki2` for instructions.
Success will look something like this::
2011-11-27 01:22:45,277 INFO [sqlalchemy.engine.base.Engine][MainThread]
PRAGMA table_info("pages")
2011-11-27 01:22:45,277 INFO [sqlalchemy.engine.base.Engine][MainThread] ()
2011-11-27 01:22:45,277 INFO [sqlalchemy.engine.base.Engine][MainThread]
CREATE TABLE pages (
id INTEGER NOT NULL,
name TEXT,
data TEXT,
PRIMARY KEY (id),
UNIQUE (name)
)
2011-11-27 01:22:45,278 INFO [sqlalchemy.engine.base.Engine][MainThread] ()
2011-11-27 01:22:45,397 INFO [sqlalchemy.engine.base.Engine][MainThread]
COMMIT
2011-11-27 01:22:45,400 INFO [sqlalchemy.engine.base.Engine][MainThread]
BEGIN (implicit)
2011-11-27 01:22:45,401 INFO [sqlalchemy.engine.base.Engine][MainThread]
INSERT INTO pages (name, data) VALUES (?, ?)
2011-11-27 01:22:45,401 INFO [sqlalchemy.engine.base.Engine][MainThread]
('FrontPage', 'This is the front page')
2011-11-27 01:22:45,402 INFO [sqlalchemy.engine.base.Engine][MainThread]
COMMIT
Viewing the Application in a Browser
------------------------------------
We can't. At this point, our system is in a "non-runnable" state; we'll need
to change view-related files in the next chapter to be able to start the
application successfully. If you try to start the application (See
:ref:`wiki2-start-the-application`), you'll wind
up with a Python traceback on your console that ends with this exception:
.. code-block:: text
ImportError: cannot import name MyModel
This will also happen if you attempt to run the tests.
|
