============== Defining Views ============== A :term:`view callable` in a :app:`Pyramid` application is typically a simple Python function that accepts a single parameter named :term:`request`. A view callable is assumed to return a :term:`response` object. The request object has a dictionary as an attribute named ``matchdict``. A ``matchdict`` maps the placeholders in the matching URL ``pattern`` to the substrings of the path in the :term:`request` URL. For instance, if a call to :meth:`pyramid.config.Configurator.add_route` has the pattern ``/{one}/{two}``, and a user visits ``http://example.com/foo/bar``, our pattern would be matched against ``/foo/bar`` and the ``matchdict`` would look like: ``{'one':'foo', 'two':'bar'}`` Declaring Dependencies in Our ``setup.py`` File =============================================== The view code in our application will depend on a package which is not a dependency of the original "tutorial" application. The original "tutorial" application was generated by the ``pcreate`` command; it doesn't know about our custom application requirements. We need to add a dependency on the ``docutils`` package to our ``tutorial`` package's ``setup.py`` file by assigning this dependency to the ``requires`` parameter in ``setup()``. Open ``tutorial/setup.py`` and edit it to look like the following: .. literalinclude:: src/views/setup.py :linenos: :language: python :emphasize-lines: 20 (Only the highlighted line needs to be added.) Running ``setup.py develop`` ============================ Since a new software dependency was added, you will need to rerun ``python setup.py develop`` inside the root of the ``tutorial`` package to obtain and register the newly added dependency distribution. Make sure your current working directory is the root of the project (the directory in which setup.py lives) and execute the following command. On UNIX: .. code-block:: text $ cd tutorial $ $VENV/bin/python setup.py develop On Windows: .. code-block:: text c:\pyramidtut> cd tutorial c:\pyramidtut\tutorial> %VENV%\Scripts\python setup.py develop Success executing this command will end with a line to the console something like:: Finished processing dependencies for tutorial==0.0 Changing the ``views.py`` File ============================== It's time for a major change. Open ``tutorial/tutorial/views.py`` and edit it to look like the following: .. literalinclude:: src/views/tutorial/views.py :linenos: :language: python :emphasize-lines: 1-7,12,15-70 (The highlighted lines are the ones that need to be added or edited.) We got rid of the ``my_view`` view function and its decorator that was added when we originally rendered the ``alchemy`` scaffold. It was only an example and isn't relevant to our application. Then we added four :term:`view callable` functions to our ``views.py`` module: * ``view_wiki()`` - Displays the wiki itself. It will answer on the root URL. * ``view_page()`` - Displays an individual page. * ``add_page()`` - Allows the user to add a page. * ``edit_page()`` - Allows the user to edit a page. We'll describe each one briefly and show the resulting ``views.py`` file afterward. .. note:: There is nothing special about the filename ``views.py``. A project may have many view callables throughout its codebase in arbitrarily-named files. Files implementing view callables often have ``view`` in their filenames (or may live in a Python subpackage of your application package named ``views``), but this is only by convention. The ``view_wiki`` view function ------------------------------- ``view_wiki()`` is the :term:`default view` that gets called when a request is made to the root URL of our wiki. It always redirects to a URL which represents the path to our "FrontPage". .. literalinclude:: src/views/tutorial/views.py :lines: 18-21 :linenos: :language: python ``view_wiki()`` returns an instance of the :class:`pyramid.httpexceptions.HTTPFound` class (instances of which implement the :class:`pyramid.interfaces.IResponse` interface like :class:`pyramid.response.Response` does). It uses the :meth:`pyramid.request.Request.route_url` API to construct a URL to the ``FrontPage`` page (e.g. ``http://localhost:6543/FrontPage``), which is used as the "location" of the ``HTTPFound`` response, forming an HTTP redirect. The ``view_page`` view function ------------------------------- ``view_page()`` is used to display a single page of our wiki. It renders the :term:`reStructuredText` body of a page (stored as the ``data`` attribute of a ``Page`` model object) as HTML. Then it substitutes an HTML anchor for each *WikiWord* reference in the rendered HTML using a compiled regular expression. .. literalinclude:: src/views/tutorial/views.py :lines: 23-43 :linenos: :language: python The ``check()`` function is used as the first argument to ``wikiwords.sub``, indicating that it should be called to provide a value for each WikiWord match found in the content. If the wiki already contains a page with the matched WikiWord name, ``check()`` generates a view link to be used as the substitution value and returns it. If the wiki does not already contain a page with the matched WikiWord name, ``check()`` generates an "add" link as the substitution value and returns it. As a result, the ``content`` variable is now a fully formed bit of HTML containing various view and add links for WikiWords based on the content of our current page object. We then generate an edit URL because it's easier to do here than in the template, and we return a dictionary with a number of arguments. The fact that ``view_page()`` returns a dictionary (as opposed to a :term:`response` object) is a cue to :app:`Pyramid` that it should try to use a :term:`renderer` associated with the view configuration to render a response. In our case, the renderer used will be the ``templates/view.pt`` template, as indicated in the ``@view_config`` decorator that is applied to ``view_page()``. The ``add_page`` view function ------------------------------ ``add_page()`` is invoked when a user clicks on a *WikiWord* which isn't yet represented as a page in the system. The ``check`` function within the ``view_page`` view generates URLs to this view. ``add_page()`` also acts as a handler for the form that is generated when we want to add a page object. The ``matchdict`` attribute of the request passed to the ``add_page()`` view will have the values we need to construct URLs and find model objects. .. literalinclude:: src/views/tutorial/views.py :lines: 45-56 :linenos: :language: python The ``matchdict`` will have a ``'pagename'`` key that matches the name of the page we'd like to add. If our add view is invoked via, e.g. ``http://localhost:6543/add_page/SomeName``, the value for ``'pagename'`` in the ``matchdict`` will be ``'SomeName'``. If the view execution *is* a result of a form submission (i.e. the expression ``'form.submitted' in request.params`` is ``True``), we scrape the page body from the form data, create a Page object with this page body and the name taken from ``matchdict['pagename']``, and save it into the database using ``DBSession.add``. We then redirect back to the ``view_page`` view for the newly created page. If the view execution is *not* a result of a form submission (i.e. the expression ``'form.submitted' in request.params`` is ``False``), the view callable renders a template. To do so, it generates a "save url" which the template uses as the form post URL during rendering. We're lazy here, so we're going to use the same template (``templates/edit.pt``) for the add view as well as the page edit view. To do so we create a dummy Page object in order to satisfy the edit form's desire to have *some* page object exposed as ``page``. :app:`Pyramid` will render the template associated with this view to a response. The ``edit_page`` view function ------------------------------- ``edit_page()`` is invoked when a user clicks the "Edit this Page" button on the view form. It renders an edit form but it also acts as the handler for the form it renders. The ``matchdict`` attribute of the request passed to the ``edit_page`` view will have a ``'pagename'`` key matching the name of the page the user wants to edit. .. literalinclude:: src/views/tutorial/views.py :lines: 58-70 :linenos: :language: python If the view execution *is* a result of a form submission (i.e. the expression ``'form.submitted' in request.params`` is ``True``), the view grabs the ``body`` element of the request parameters and sets it as the ``data`` attribute of the page object. It then redirects to the ``view_page`` view of the wiki page. If the view execution is *not* a result of a form submission (i.e. the expression ``'form.submitted' in request.params`` is ``False``), the view simply renders the edit form, passing the page object and a ``save_url`` which will be used as the action of the generated form. Adding Templates ================ The ``view_page``, ``add_page`` and ``edit_page`` views that we've added reference a :term:`template`. Each template is a :term:`Chameleon` :term:`ZPT` template. These templates will live in the ``templates`` directory of our tutorial package. Chameleon templates must have a ``.pt`` extension to be recognized as such. The ``view.pt`` Template ------------------------ Create ``tutorial/tutorial/templates/view.pt`` and add the following content: .. literalinclude:: src/views/tutorial/templates/view.pt :linenos: :language: xml This template is used by ``view_page()`` for displaying a single wiki page. It includes: - A ``div`` element that is replaced with the ``content`` value provided by the view (rows 45-47). ``content`` contains HTML, so the ``structure`` keyword is used to prevent escaping it (i.e. changing ">" to ">", etc.) - A link that points at the "edit" URL which invokes the ``edit_page`` view for the page being viewed (rows 49-51). The ``edit.pt`` Template ------------------------ Create ``tutorial/tutorial/templates/edit.pt`` and add the following content: .. literalinclude:: src/views/tutorial/templates/edit.pt :linenos: :language: xml This template is used by ``add_page()`` and ``edit_page()`` for adding and editing a wiki page. It displays a page containing a form that includes: - A 10 row by 60 column ``textarea`` field named ``body`` that is filled with any existing page data when it is rendered (rows 46-47). - A submit button that has the name ``form.submitted`` (row 48). The form POSTs back to the "save_url" argument supplied by the view (row 45). The view will use the ``body`` and ``form.submitted`` values. .. note:: Our templates use a ``request`` object that none of our tutorial views return in their dictionary. ``request`` is one of several names that are available "by default" in a template when a template renderer is used. See :ref:`renderer_system_values` for information about other names that are available by default when a template is used as a renderer. Static Assets ------------- Our templates name a single static asset named ``pylons.css``. We don't need to create this file within our package's ``static`` directory because it was provided at the time we created the project. This file is a little too long to replicate within the body of this guide, however it is available `online `_. This CSS file will be accessed via e.g. ``http://localhost:6543/static/pylons.css`` by virtue of the call to ``add_static_view`` directive we've made in the ``__init__.py`` file. Any number and type of static assets can be placed in this directory (or subdirectories) and are just referred to by URL or by using the convenience method ``static_url`` e.g. ``request.static_url('{{package}}:static/foo.css')`` within templates. Adding Routes to ``__init__.py`` ================================ The ``__init__.py`` file contains :meth:`pyramid.config.Configurator.add_route` calls which serve to add routes to our application. First, we’ll get rid of the existing route created by the template using the name ``'home'``. It’s only an example and isn’t relevant to our application. We then need to add four calls to ``add_route``. Note that the *ordering* of these declarations is very important. ``route`` declarations are matched in the order they're found in the ``__init__.py`` file. #. Add a declaration which maps the pattern ``/`` (signifying the root URL) to the route named ``view_wiki``. It maps to our ``view_wiki`` view callable by virtue of the ``@view_config`` attached to the ``view_wiki`` view function indicating ``route_name='view_wiki'``. #. Add a declaration which maps the pattern ``/{pagename}`` to the route named ``view_page``. This is the regular view for a page. It maps to our ``view_page`` view callable by virtue of the ``@view_config`` attached to the ``view_page`` view function indicating ``route_name='view_page'``. #. Add a declaration which maps the pattern ``/add_page/{pagename}`` to the route named ``add_page``. This is the add view for a new page. It maps to our ``add_page`` view callable by virtue of the ``@view_config`` attached to the ``add_page`` view function indicating ``route_name='add_page'``. #. Add a declaration which maps the pattern ``/{pagename}/edit_page`` to the route named ``edit_page``. This is the edit view for a page. It maps to our ``edit_page`` view callable by virtue of the ``@view_config`` attached to the ``edit_page`` view function indicating ``route_name='edit_page'``. As a result of our edits, the ``__init__.py`` file should look something like: .. literalinclude:: src/views/tutorial/__init__.py :linenos: :language: python :emphasize-lines: 19-22 (The highlighted lines are the ones that need to be added or edited.) Viewing the Application in a Browser ==================================== We can finally examine our application in a browser (See :ref:`wiki2-start-the-application`). Launch a browser and visit each of the following URLs, check that the result is as expected: - http://localhost:6543 in a browser invokes the ``view_wiki`` view. This always redirects to the ``view_page`` view of the FrontPage page object. - http://localhost:6543/FrontPage in a browser invokes the ``view_page`` view of the front page object. - http://localhost:6543/FrontPage/edit_page in a browser invokes the edit view for the front page object. - http://localhost:6543/add_page/SomePageName in a browser invokes the add view for a page. - To generate an error, visit http://localhost:6543/foobars/edit_page which will generate a ``NoResultFound: No row was found for one()`` error. You'll see an interactive traceback facility provided by :term:`pyramid_debugtoolbar`.