============ Basic Layout ============ The starter files generated by the ``pyramid_routesalchemy`` scaffold 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/ `_. 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. The generated ``development.ini`` file is read by ``pserve`` which looks for the application module in the ``use`` variable of the ``app:main`` section. The *entry point* is defined in the Setuptools configuration of this module, specifically in the ``setup.py`` file. For this tutorial, the *entry point* is defined as ``tutorial:main`` and points to a function named ``main``. First we need some imports to support later code: .. literalinclude:: src/basiclayout/tutorial/__init__.py :end-before: main :linenos: :language: py Next we define the main function and create a SQLAlchemy database engine from the ``sqlalchemy.`` prefixed settings in the ``development.ini`` file's ``[app:main]`` section. This will be a URI (something like ``sqlite://``): .. literalinclude:: src/basiclayout/tutorial/__init__.py :lines: 6-9 :linenos: :language: py We then initialize our SQL database using SQLAlchemy, passing it the engine: .. literalinclude:: src/basiclayout/tutorial/__init__.py :lines: 10 :language: py The next step is to construct a :term:`Configurator`: .. literalinclude:: src/basiclayout/tutorial/__init__.py :lines: 11 :language: py ``settings`` is passed to the Configurator as a keyword argument with the dictionary values passed by PasteDeploy as the ``**settings`` argument. This will be a dictionary of settings parsed from the ``.ini`` file, which contains deployment-related values such as ``pyramid.reload_templates``, ``db_string``, etc. We now can call :meth:`pyramid.config.Configurator.add_static_view` with the arguments ``static`` (the name), and ``tutorial:static`` (the path): .. literalinclude:: src/basiclayout/tutorial/__init__.py :lines: 12 :language: py 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. Using the configurator we can also register a :term:`route configuration` via the :meth:`pyramid.config.Configurator.add_route` method that will be used when the URL is ``/``: .. literalinclude:: src/basiclayout/tutorial/__init__.py :lines: 13 :language: py Since this route has a ``pattern`` equalling ``/`` it is the route that will be matched when the URL ``/`` is visted, e.g. ``http://localhost:6543/``. Mapping the ``home`` route to code is done by registering a view. You will use :meth:`pyramid.config.Configurator.add_view` in :term:`URL dispatch` to register views for the routes, mapping your patterns to code: .. literalinclude:: src/basiclayout/tutorial/__init__.py :lines: 14-15 :language: py The first positional ``add_view`` argument ``tutorial.views.my_view`` is the dotted name to a *function* we write (generated by the ``pyramid_routesalchemy`` scaffold) that is given a ``request`` object and which returns a response or a dictionary. This view also names a ``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. Finally, we use the :meth:`pyramid.config.Configurator.make_wsgi_app` method to return a :term:`WSGI` application: .. literalinclude:: src/basiclayout/tutorial/__init__.py :lines: 16 :language: py Our final ``__init__.py`` file will look like this: .. literalinclude:: src/basiclayout/tutorial/__init__.py :linenos: :language: py 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`` scaffold put the classes that implement our models. Let's take a look. First, we need some imports to support later code. .. literalinclude:: src/basiclayout/tutorial/models.py :end-before: DBSession :linenos: :language: py Next we set up a SQLAlchemy "DBSession" object: .. literalinclude:: src/basiclayout/tutorial/models.py :lines: 15-16 :linenos: :language: py We also need to create a declarative ``Base`` object to use as a base class for our model: .. literalinclude:: src/basiclayout/tutorial/models.py :lines: 17 :language: py To give a simple example of a model class, we define one named ``MyModel``: .. literalinclude:: src/basiclayout/tutorial/models.py :pyobject: MyModel :linenos: :language: py Our sample model 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. Next we define a function named ``populate`` which adds a single model instance into our SQL storage and commits a transaction: .. literalinclude:: src/basiclayout/tutorial/models.py :pyobject: populate :linenos: :language: py The function doesn't do a lot in this case, but it's there to illustrate how an application requiring many objects to be set up could work. Lastly we have 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. This is the initialization function that is called from __init__.py above. .. literalinclude:: src/basiclayout/tutorial/models.py :pyobject: initialize_sql :linenos: :language: py Here is the complete source for ``models.py``: .. literalinclude:: src/basiclayout/tutorial/models.py :linenos: :language: py