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Extending the page & title models
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.. versionadded:: 3.0

You can extend the page and title models with your own fields (e.g. adding
an icon for every page) by using the extension models:
``cms.extensions.PageExtension`` and ``cms.extensions.TitleExtension``,
respectively.

******
How To
******

To add a field to the page model, create a class that inherits from
``cms.extensions.PageExtension``. Make sure to import the
``cms.extensions.PageExtension`` model. Your class should live in one of your
apps' ``models.py`` (or module). Since ``PageExtension`` (and
``TitleExtension``) inherit from ``django.db.models.Model``, you are free to
add any field you want but make sure you don't use a unique constraint on any
of your added fields because uniqueness prevents the copy mechanism of the
extension from working correctly. This means that you can't use one-to-one
relations on the extension model. Finally, you'll need to register the model
with using ``extension_pool``.

Here's a simple example which adds an ``icon`` field to the page::

    from django.db import models

    from cms.extensions import PageExtension
    from cms.extensions.extension_pool import extension_pool


    class IconExtension(PageExtension):
        image = models.ImageField(upload_to='icons')

    extension_pool.register(IconExtension)


Hooking the extension to the admin site
=======================================

To make your extension editable, you must first create an admin class that
subclasses ``cms.extensions.PageExtensionAdmin``. This admin handles page
permissions. If you want to use your own admin class, make sure to exclude the
live versions of the extensions by using
``filter(extended_page__publisher_is_draft=True)`` on the queryset.

Continuing with the example model above, here's a simple corresponding
``PageExtensionAdmin`` class::

    from django.contrib import admin
    from cms.extensions import PageExtensionAdmin

    from .models import IconExtension


    class IconExtensionAdmin(PageExtensionAdmin):
        pass

    admin.site.register(IconExtension, IconExtensionAdmin)


Since PageExtensionAdmin inherits from ModelAdmin, you'll be able to use the
normal set of Django ModelAdmin properties, as appropriate to your
circumstance.

Once you've registered your admin class, a new model will appear in the top-
level admin list.

Note that the field that holds the relationship between the extension and a
CMS Page is non-editable, so it will not appear in the admin views. This,
unfortunately, leaves the operator without a means of "attaching" the page
extension to the correct pages. The way to address this is to use a
CMSToolbar.


Adding a Toolbar Menu Item for your Page extension
==================================================

You'll also want to make your model editable from the cms toolbar in order to
associate each instance of the extension model with a page. (Page isn't an
editable attribute in the default admin interface.) The following example,
which should live in a file named ``cms_toolbar.py`` in one of your apps, adds
a menu entry for the extension on each page::

    from cms.api import get_page_draft
    from cms.toolbar_pool import toolbar_pool
    from cms.toolbar_base import CMSToolbar
    from cms.utils import get_cms_setting
    from cms.utils.permissions import has_page_change_permission
    from django.core.urlresolvers import reverse, NoReverseMatch
    from django.utils.translation import ugettext_lazy as _
    from .models import IconExtension


    @toolbar_pool.register
    class IconExtensionToolbar(CMSToolbar):
        def populate(self):
            # always use draft if we have a page
            self.page = get_page_draft(self.request.current_page)

            if not self.page:
                # Nothing to do
                return

            # check global permissions if CMS_PERMISSIONS is active
            if get_cms_setting('PERMISSION'):
                has_global_current_page_change_permission = has_page_change_permission(self.request)
            else:
                has_global_current_page_change_permission = False
                # check if user has page edit permission
            can_change = self.request.current_page and self.request.current_page.has_change_permission(self.request)
            if has_global_current_page_change_permission or can_change:
                try:
                    icon_extension = IconExtension.objects.get(extended_object_id=self.page.id)
                except IconExtension.DoesNotExist:
                    icon_extension = None
                try:
                    if icon_extension:
                        url = reverse('admin:myapp_iconextension_change', args=(icon_extension.pk,))
                    else:
                        url = reverse('admin:myapp_iconextension_add') + '?extended_object=%s' % self.page.pk
                except NoReverseMatch:
                    # not in urls
                    pass
                else:
                    not_edit_mode = not self.toolbar.edit_mode
                    current_page_menu = self.toolbar.get_or_create_menu('page')
                    current_page_menu.add_modal_item(_('Page Icon'), url=url, disabled=not_edit_mode)


Now when the operator invokes "Edit this page..." from the toolbar, there will
be an additional menu item ``Page Icon ...`` (in this case), which can be used
to open a modal dialog where the operator can affect the new ``icon`` field.

Note that when the extension is saved, the corresponding page is marked as
having unpublished changes. To see the new extension values make sure to
publish the page.


Using extensions with menus
===========================

If you want the extension to show up in the menu (e.g. if you had created an
extension that added an icon to the page) use menu modifiers. Every ``node.id``
corresponds to their related ``page.id``. ``Page.objects.get(pk=node.id)`` is
the way to get the page object. Every page extension has a one-to-one
relationship with the page so you can access it by using the reverse relation,
e.g. ``extension = page.yourextensionlowercased``. Now you can hook this
extension by storing it on the node: ``node.extension = extension``. In the
menu template you can access your icon on the child object:
``child.extension.icon``.


Using extensions in templates
=============================

To access a page extension in page templates you can simply access the
approriate related_name field that is now available on the Page object.

As per normal Django defaul related_name naming mechanism, the appropriate
field to access is the same as your PageExtension model name, but lowercased.
Assuming your Page Extension model class is ``IconExtension``, the
relationship to the page extension will be available on
``page.iconextension``, so you can use something like::

    {% load staticfiles %}

    {# rest of template omitted ... #}

    {% if request.current_page.iconextension %}
        <img src="{% static request.current_page.iconextension.url %}">
    {% endif %}

Where ``request.current_page`` is the way to access the current page that is
rendering the template.

It is important to remember that unless the operator has already assigned a
page extension to every page, a page may not have the iconextension
relationship available, hence the use of the ``{% if ... %}...{% endif %}``
above.


Handling relations
==================

If your PageExtension or TitleExtension includes a ForeignKey *from* another
model or includes a ManyToMany field, you should also override the method
``copy_relations(self, oldinstance, language)`` so that these fields are
copied appropriately when the CMS makes a copy of your extension to support
versioning, etc.


Here's an example that uses a `ManyToMany`` field::

    from django.db import models
    from cms.extensions import PageExtension
    from cms.extensions.extension_pool import extension_pool


    class MyPageExtension(PageExtension):

        page_categories = models.ManyToMany('categories.Category', blank=True, null=True)

        def copy_relations(self, oldinstance, language):
            for page_category in oldinstance.page_categories.all():
                page_category.pk = None
                page_category.mypageextension = self
                page_category.save()

    extension_pool.register(MyPageExtension)
