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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.
Edit ``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: 20-22,24,25
The highlighted lines are the ones that need to be changed, as well as
removing lines that reference ``Index``.
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: 14,31,36
Only the highlighted lines need to be changed, as well as removing the lines
referencing ``pyramid.scripts.common`` and ``options`` under the ``main``
function.
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::
2015-05-24 15:34:14,542 INFO [sqlalchemy.engine.base.Engine:1192][MainThread] SELECT CAST('test plain returns' AS VARCHAR(60)) AS anon_1
2015-05-24 15:34:14,542 INFO [sqlalchemy.engine.base.Engine:1193][MainThread] ()
2015-05-24 15:34:14,543 INFO [sqlalchemy.engine.base.Engine:1192][MainThread] SELECT CAST('test unicode returns' AS VARCHAR(60)) AS anon_1
2015-05-24 15:34:14,543 INFO [sqlalchemy.engine.base.Engine:1193][MainThread] ()
2015-05-24 15:34:14,543 INFO [sqlalchemy.engine.base.Engine:1097][MainThread] PRAGMA table_info("pages")
2015-05-24 15:34:14,544 INFO [sqlalchemy.engine.base.Engine:1100][MainThread] ()
2015-05-24 15:34:14,544 INFO [sqlalchemy.engine.base.Engine:1097][MainThread]
CREATE TABLE pages (
id INTEGER NOT NULL,
name TEXT,
data TEXT,
PRIMARY KEY (id),
UNIQUE (name)
)
2015-05-24 15:34:14,545 INFO [sqlalchemy.engine.base.Engine:1100][MainThread] ()
2015-05-24 15:34:14,546 INFO [sqlalchemy.engine.base.Engine:686][MainThread] COMMIT
2015-05-24 15:34:14,548 INFO [sqlalchemy.engine.base.Engine:646][MainThread] BEGIN (implicit)
2015-05-24 15:34:14,549 INFO [sqlalchemy.engine.base.Engine:1097][MainThread] INSERT INTO pages (name, data) VALUES (?, ?)
2015-05-24 15:34:14,549 INFO [sqlalchemy.engine.base.Engine:1100][MainThread] ('FrontPage', 'This is the front page')
2015-05-24 15:34:14,550 INFO [sqlalchemy.engine.base.Engine:686][MainThread] COMMIT
View 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.
|
