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+Views
+-----
+
+This chapter aims to describe the concept of a `view` used all along
+the development of a web application and how it has been implemented
+in `CubicWeb`.
+
+We'll start with a description of the interface providing you with a basic
+understanding of the classes and methods available, then detail the view
+selection principle which makes `CubicWeb` web interface very flexible.
+
+A `View` is an object applied to another object such as an entity.
+
+Basic class for views
+---------------------
+
+Class `View` (`cubicweb.view`)
+`````````````````````````````````````
+
+This class is an abstraction of a view class, used as a base class for every
+renderable object such as views, templates, graphic components, etc.
+
+A `View` is instantiated to render a result set or part of a result set. `View`
+subclasses may be parametrized using the following class attributes:
+
+ * `templatable` indicates if the view may be embeded in a main
+ template or if it has to be rendered standalone (i.e. XML views
+ must not be embeded in the main template for HTML pages)
+ * if the view is not templatable, it should set the `content_type` class
+ attribute to the correct MIME type (text/xhtml by default)
+ * the `category` attribute may be used in the interface to regroup related
+ objects together
+
+At instantiation time, the standard `req`, `rset`, and `cursor`
+attributes are added and the `w` attribute will be set at rendering
+time.
+
+A view writes to its output stream thanks to its attribute `w` (`UStreamIO`).
+
+The basic interface for views is as follows (remember that the result set has a
+tabular structure with rows and columns, hence cells):
+
+* `dispatch(**context)`, render the view by calling `call` or
+ `cell_call` depending on the given parameters
+* `call(**kwargs)`, call the view for a complete result set or null (default
+ implementation calls `cell_call()` on each cell of the result set)
+* `cell_call(row, col, **kwargs)`, call the view for a given cell of a result set
+* `url()`, returns the URL enabling us to get the view with the current
+ result set
+* `view(__vid, rset, __fallback_vid=None, **kwargs)`, call the view of identifier
+ `__vid` on the given result set. It is possible to give a view identifier
+ of fallback that will be used if the view requested is not applicable to the
+ result set
+
+* `wview(__vid, rset, __fallback_vid=None, **kwargs)`, similar to `view` except
+ the flow is automatically passed in the parameters
+
+* `html_headers()`, returns a list of HTML headers to set by the main template
+
+* `page_title()`, returns the title to use in the HTML header `title`
+
+
+Other basic view classes
+````````````````````````
+Here are some of the subclasses of `View` defined in `cubicweb.common.view`
+that are more concrete as they relate to data rendering within the application:
+
+* `EntityView`, view applying to lines or cell containing an entity (e.g. an eid)
+* `StartupView`, start view that does not require a result set to apply to
+* `AnyRsetView`, view applied to any result set
+* `EmptyRsetView`, view applied to an empty result set
+
+
+Examples of views class
+-----------------------
+
+- Using `templatable`, `content_type` and HTTP cache configuration
+
+.. code-block:: python
+
+
+ class RSSView(XMLView):
+ id = 'rss'
+ title = _('rss')
+ templatable = False
+ content_type = 'text/xml'
+ http_cache_manager = MaxAgeHTTPCacheManager
+ cache_max_age = 60*60*2 # stay in http cache for 2 hours by default
+
+
+
+- Using custom selector
+
+.. code-block:: python
+
+
+ class SearchForAssociationView(EntityView):
+ """view called by the edition view when the user asks
+ to search for something to link to the edited eid
+ """
+ id = 'search-associate'
+ title = _('search for association')
+ __select__ = one_line_rset() & match_search_state('linksearch') & implements('Any')
+
+
+Example of a view customization
+-------------------------------
+
+[FIXME] XXX Example needs to be rewritten as it shows how to modify cell_call which
+contredicts our advise of not modifying it.
+
+We'll show you now an example of a ``primary`` view and how to customize it.
+
+If you want to change the way a ``BlogEntry`` is displayed, just override
+the method ``cell_call()`` of the view ``primary`` in ``BlogDemo/views.py`` ::
+
+.. code-block:: python
+
+ from cubicweb.view import EntityView
+ from cubicweb.selectors import implements
+
+ class BlogEntryPrimaryView(EntityView):
+ id = 'primary'
+ __select__ =implements('Blog')
+
+ def cell_call(self, row, col):
+ entity = self.entity(row, col)
+ self.w(u'<h1>%s</h1>' % entity.title)
+ self.w(u'<p>published on %s in category %s</p>' % \
+ (entity.publish_date.strftime('%Y-%m-%d'), entity.category))
+ self.w(u'<p>%s</p>' % entity.text)
+
+The above source code defines a new primary view (`line 03`) for
+``BlogEntry`` (`line 05`).
+
+Since views are applied to result sets which can be tables of
+data, we have to recover the entity from its (row,col)-coordinates (`line 08`).
+We will get to this in more detail later.
+
+The view method ``self.w()`` is used to output data. Here `lines
+09-12` output HTML tags and values of the entity's attributes.
+
+When displaying the same blog entry as before, you will notice that the
+page is now looking much nicer. [FIXME: it is not clear to what this refers.]
+
+.. image:: ../../images/lax-book.09-new-view-blogentry.en.png
+ :alt: blog entries now look much nicer
+
+Let us now improve the primary view of a blog
+
+.. code-block:: python
+
+ class BlogPrimaryView(EntityView):
+ id = 'primary'
+ __select__ =implements('Blog')
+
+ def cell_call(self, row, col):
+ entity = self.entity(row, col)
+ self.w(u'<h1>%s</h1>' % entity.title)
+ self.w(u'<p>%s</p>' % entity.description)
+ rset = self.req.execute('Any E WHERE E entry_of B, B eid "%s"' % entity.eid)
+ self.wview('primary', rset)
+
+In the above source code, `lines 01-08` are similar to the previous
+view we defined. [FIXME: defined where ?]
+
+At `line 09`, a simple request is made to build a result set with all
+the entities linked to the current ``Blog`` entity by the relationship
+``entry_of``. The part of the framework handling the request knows
+about the schema and infer that such entities have to be of the
+``BlogEntry`` kind and retrieves them.
+
+The request returns a selection of data called a result set. At
+`line 10` the view 'primary' is applied to this result set to output
+HTML.
+
+**This is to be compared to interfaces and protocols in object-oriented
+languages. Applying a given view called 'a_view' to all the entities
+of a result set only requires to have for each entity of this result set,
+an available view called 'a_view' which accepts the entity.**
+
+Assuming we added entries to the blog titled `MyLife`, displaying it
+now allows to read its description and all its entries.
+
+.. image:: ../../images/lax-book.10-blog-with-two-entries.en.png
+ :alt: a blog and all its entries
+
+**Before we move forward, remember that the selection/view principle is
+at the core of `CubicWeb`. Everywhere in the engine, data is requested
+using the RQL language, then HTML/XML/text/PNG is output by applying a
+view to the result set returned by the query. That is where most of the
+flexibility comes from.**
+
+[WRITE ME]
+
+* implementing interfaces, calendar for blog entries
+* show that a calendar view can export data to ical
+
+We will implement the `cubicweb.interfaces.ICalendarable` interfaces on
+entities.BlogEntry and apply the OneMonthCalendar and iCalendar views
+to result sets like "Any E WHERE E is BlogEntry"
+
+* create view "blogentry table" with title, publish_date, category
+
+We will show that by default the view that displays
+"Any E,D,C WHERE E publish_date D, E category C" is the table view.
+Of course, the same can be obtained by calling
+self.wview('table',rset)
+
+* in view blog, select blogentries and apply view "blogentry table"
+* demo ajax by filtering blogentry table on category
+
+we did the same with 'primary', but with tables we can turn on filters
+and show that ajax comes for free.
+[FILLME]
+
+
+
+XML views, binaries...
+----------------------
+For views generating other formats than HTML (an image generated dynamically
+for example), and which can not simply be included in the HTML page generated
+by the main template (see above), you have to:
+
+* set the attribute `templatable` of the class to `False`
+* set, through the attribute `content_type` of the class, the MIME type generated
+ by the view to `application/octet-stream`
+
+For views dedicated to binary content creation (like dynamically generated
+images), we have to set the attribute `binary` of the class to `True` (which
+implies that `templatable == False`, so that the attribute `w` of the view could be
+replaced by a binary flow instead of unicode).