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============
Basic Layout
============
The starter files generated by the ``pyramid_routesalchemy`` template
are basic, but they provide a good orientation for the high-level
patterns common to most :term:`url dispatch` -based :app:`Pyramid`
projects.
The source code for this tutorial stage can be browsed at
`http://github.com/Pylons/pyramid/tree/master/docs/tutorials/wiki2/src/basiclayout/
<http://github.com/Pylons/pyramid/tree/master/docs/tutorials/wiki2/src/basiclayout/>`_.
App Startup with ``__init__.py``
--------------------------------
A directory on disk can be turned into a Python :term:`package` by containing
an ``__init__.py`` file. Even if empty, this marks a directory as a Python
package. We use ``__init__.py`` both as a package marker and to contain
configuration code.
When you run the application using the ``paster`` command using the
``development.ini`` generated config file, the application configuration
points at an Setuptools *entry point* described as ``egg:tutorial#app``. In
our application, because the application's ``setup.py`` file says so, this
entry point happens to be the ``app`` function within the file named
``__init__.py``:
.. literalinclude:: src/basiclayout/tutorial/__init__.py
:linenos:
:language: py
#. *Lines 1-4*. Imports to support later code.
#. *Line 9*. Create a SQLAlchemy database engine from the ``sqlalchemy.``
prefixed settings in the ``development.ini`` file's ``[app:tutorial]``
section. This will be a URI (something like ``sqlite://``).
#. *Line 10*. We initialize our SQL database using SQLAlchemy, passing
it the engine
#. *Line 11*. We construct a :term:`Configurator`. ``settings`` is
passed as a keyword argument with the dictionary values passed by
PasteDeploy as the ``settings`` argument. This will be a
dictionary of settings parsed by PasteDeploy, which contains
deployment-related values such as ``reload_templates``,
``db_string``, etc.
#. *Line 12*. We call
:meth:`pyramid.configuration.Configurator.add_static_view` with the
arguments ``static`` (the name), and ``tutorial:static`` (the path). This
registers a static resource view which will match any URL that starts with
``/static/``. This will serve up static resources for us from within the
``static`` directory of our ``tutorial`` package, in this case,
via ``http://localhost:6543/static/`` and below. With this declaration,
we're saying that any URL that starts with ``/static`` should go to the
static view; any remainder of its path (e.g. the ``/foo`` in
``/static/foo``) will be used to compose a path to a static file resource,
such as a CSS file.
#. *Lines 13-14*. Register a :term:`route configuration` via the
:meth:`pyramid.configuration.Configurator.add_route` method that will be
used when the URL is ``/``. Since this route has an ``pattern`` equalling
``/`` it is the "default" route. The argument named ``view`` with the
value ``tutorial.views.my_view`` is the dotted name to a *function* we
write (generated by the ``pyramid_routesalchemy`` template) that is given
a ``request`` object and which returns a response or a dictionary. You
will use :meth:`pyramid.configuration.Configurator.add_route` statements
in a :term:`URL dispatch` based application to map URLs to code. This
route also names a ``view_renderer``, which is a template which lives in
the ``templates`` subdirectory of the package. When the
``tutorial.views.my_view`` view returns a dictionary, a :term:`renderer`
will use this template to create a response.
#. *Line 15*. We use the
:meth:`pyramid.configuration.Configurator.make_wsgi_app` method to return
a :term:`WSGI` application.
Content Models with ``models.py``
---------------------------------
In a SQLAlchemy-based application, a *model* object is an object
composed by querying the SQL database which backs an application.
SQLAlchemy is an "object relational mapper" (an ORM). The
``models.py`` file is where the ``pyramid_routesalchemy`` Paster
template put the classes that implement our models.
Here is the source for ``models.py``:
.. literalinclude:: src/basiclayout/tutorial/models.py
:linenos:
:language: py
#. *Lines 1-13*. Imports to support later code.
#. *Line 15*. We set up a SQLAlchemy "DBSession" object here. We
specify that we'd like to use the "ZopeTransactionExtension". This
extension is an extension which allows us to use a *transaction
manager* instead of controlling commits and aborts to database
operations by hand.
#. *Line 16*. We create a declarative ``Base`` object to use as a
base class for our model.
#. *Lines 18-26*. A model class named ``MyModel``. It has an
``__init__`` that takes a two arguments (``name``, and ``value``).
It stores these values as ``self.name`` and ``self.value`` within
the ``__init__`` function itself. The ``MyModel`` class also has a
``__tablename__`` attribute. This informs SQLAlchemy which table
to use to store the data representing instances of this class.
#. *Lines 28-33*. A function named ``populate`` which adds a single
model instance into our SQL storage and commits a transaction.
#. *Lines 35-42*. A function named ``initialize_sql`` which receives a SQL
database engine and binds it to our SQLAlchemy DBSession object. It also
calls the ``populate`` function, to do initial database population.
|
