source: main/waeup.kofa/trunk/src/waeup/kofa/doctests/breadcrumbs.txt @ 17952

Breadcrumbs
***********

We use an adapter approach to get a flexible system of creating and
retrieving breadcrumbs for certain views.


How to get existing breadcrumbs
===============================

We create a university to check the breadcrumb functionality.

    >>> from waeup.kofa.app import University
    >>> root = getRootFolder()
    >>> root['app'] = University()
    >>> app = root['app']

The quick way (if you have a viewname)
--------------------------------------

We can get an ordered list of breadcrumbs for a given context and
viewname:

    >>> from waeup.kofa.browser.breadcrumbs import getBreadcrumbList
    >>> blist1 = getBreadcrumbList(app, 'index')
    >>> blist1
    [<waeup.kofa.browser.breadcrumbs.UniversityBreadcrumb object at 0x...>]

A slightly more extensive list for the datacenter:

    >>> blist2 = getBreadcrumbList(app['datacenter'], 'index')
    >>> from pprint import pprint
    >>> pprint(blist2)
    [<waeup.kofa.browser.breadcrumbs.UniversityBreadcrumb object at 0x...>,
     <waeup.kofa.browser.breadcrumbs.AdministrationBreadcrumb object at 0x...>,
     <waeup.kofa.browser.breadcrumbs.DataCenterBreadcrumb object at 0x...>]

We get a breadcrumb for university, administration area and data
center in that order.

Each breadcrumb provides a ``title``, ``context``, and ``viewname``
attribute, so that views and page templates can easily create markup
out of it:

     >>> pprint([(x.title) for x in blist2])
     [u'Home', u'Administration', u'Data Center']

     >>> pprint([(x.context, x.viewname) for x in blist2])
     [(<waeup.kofa.app.University object at 0x...>, 'index'),
      (<waeup.kofa.app.University object at 0x...>, 'administration'),
      (<waeup.kofa.datacenter.DataCenter object at 0x...>, 'index')]

The administration area breadcrumb might be a surprise, as there is no
equivalent object in the ZODB. In fact the administration area is only
a certain view (the 'administration' view) on the university object.

We will show below, how you can define breadcrumbs this way.

As a rule of thumb you should know, that every breadcrumb is not only
attached for a certain kind of object, but for a tuple of context
object and a viewname.

This way we can make sure, that there are different breadcrumb lists
generated for instance for the administration view of University
instances and the index view. While the first should look something
like::

  Home -> Administration

we expect for the latter only::

  Home


Another quick way (if you have a complete view)
-----------------------------------------------

Another quick approach for use in viewlets, views and similar
contexts, where you usually have a view available but not a viewname,
is to use ``getBreadcrumbListForView``.

We create a view (a page in this case, but pages are views) on the
user administration index page:

    >>> from zope.publisher.browser import TestRequest
    >>> from zope.component import getMultiAdapter
    >>> page = getMultiAdapter((app['users'], TestRequest()), name='index')

Now we can get the breadcrumbs for this view:

    >>> from waeup.kofa.browser.breadcrumbs import getBreadcrumbListForView
    >>> blist3 = getBreadcrumbListForView(page)
    >>> [x.title for x in blist3]
    [u'Home', u'Administration', u'Officers']

..note:: This works only for views created with grokcore.component
         (i.e. Grok Views, Pages, etc.) but not for simple Zope3
         views, as the viewname can not easily be extracted from the
         view for the latter ones.


Type-safe retrieval of breadcrumbs for a view
---------------------------------------------

If you want to make sure, that a view for which you want to get
breadcrumbs is really a Grok view, then you can use the
IBreadcrumbContainer adapter. This one adapts only grok views.

The returned breadcrumb container supports iteration:

    >>> from waeup.kofa.browser.interfaces import IBreadcrumbContainer
    >>> mybccontainer = IBreadcrumbContainer(page)
    >>> [x.title for x in mybccontainer]
    [u'Home', u'Administration', u'Officers']

It is, however, not a real Python list but only an iterable
container. You can also get the real list of breadcrumbs:

    >>> pprint(mybccontainer.getList())
    [<...breadcrumbs.UniversityBreadcrumb object at 0x...>,
     <...breadcrumbs.AdministrationBreadcrumb object at 0x...>,
     <...breadcrumbs.UsersContainerBreadcrumb object at 0x...>]



The general details
-------------------

Now we can get breadcrumbs for contexts and view names. For example a
breadcrumb for the 'index' view of our University object:

    >>> from zope.component import getAdapter
    >>> from waeup.kofa.browser.interfaces import IBreadcrumb
    >>> b1 = getAdapter(app, IBreadcrumb, 'index')
    >>> b1
    <waeup.kofa.browser.breadcrumbs.UniversityBreadcrumb object at 0x...>

Breadcrumb objects provide a title:

    >>> b1.title
    u'Home'

a parent (None for the app object):

    >>> b1.parent is None
    True

and a viewname:

    >>> b1.viewname
    'index'

Using a context and a viewname, one can easily compute a complete URL
in views, viewlets, etc.

    >>> b2 = getAdapter(app['datacenter'], IBreadcrumb, 'index')
    >>> b2
    <waeup.kofa.browser.breadcrumbs.DataCenterBreadcrumb object at 0x...>

    >>> b2.title
    u'Data Center'

    >>> b2.viewname
    'index'

As the data center is not root of the hierarchy, it provides a
non-trivial parent:

    >>> b2.parent
    (<waeup.kofa.app.University object at 0x...>, 'administration')

This result denotes a new context object (the University instance we
created above) and a view name ('administration').

Normally, the view name would be 'index', but as some administrative
components should look to the user as if they were grouped in a common
subarea of the root (the administration area), we can also set a
different view than the default as target.

When we like to receive the breadcrumb for this parent, we can do so
as above:

    >>> context, viewname = b2.parent
    >>> b3 = getAdapter(context, IBreadcrumb, viewname)
    >>> b3
    <waeup.kofa...breadcrumbs.AdministrationBreadcrumb object at 0x...>

As you can see, we get an AdministrationBreadcrumb, although the
context object, for which the breadcrumb was created is also the
University instance as above:

    >>> b3.context is b1.context
    True

This administration area now has still a parent, the front-page:

    >>> context, viewname = b3.parent
    >>> context, viewname
    (<waeup.kofa.app.University object at 0x...>, 'index')

We create last breadcrumb:

    >>> b4 = getAdapter(context, IBreadcrumb, viewname)

This is finally the last piece, the breadcrumb which links to the
front page. It has no parent:

    >>> b4.parent is None
    True


How to create new breadcrumbs
=============================

Breadcrumbs are looked up as named adapters. This means, you must
create a named adapter with the following specifications:

 * Derive your breadcrumb class from ``Breadcrumb`` class. This will
   save you lots of work.

 * The adapter context (``grok.context``) must be the object type you
   want to provide a breadcrumb for. So, if you want to write a
   Breadcrumb adapter for objects providing ``IMyFunnyType``, write::

     grok.context(IMyFunnyType)

 * The adapter name (``grok.name``) must be the same as the name of
   the view, for which the breadcrumb component should be
   registered. 

   If you want to write a breadcrumb component for the 'index' view of
   some content type and derive your class from Breadcrumb, then you
   can skip this step as 'index' is the default name.

 * Set a ``title`` attribute to give the text that should be
   displayed. Use something like::

     @property
     def title(self):
       return self.some_computed_title()

   if you want computed titles.