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Content Architecture

Mezzanine primarily revolves around the models found in two packages, mezzanine.core and mezzanine.pages. This section describes these models and how to extend them to create your own custom content for a Mezzanine site.

The Page Model

The foundation of a Mezzanine site is the model mezzanine.pages.models.Page. Each Page instance is stored in a hierarchical tree to form the site's navigation, and an interface for managing the structure of the navigation tree is provided in the admin via mezzanine.pages.admin.PageAdmin. All types of content inherit from the Page model and Mezzanine provides a default content type via the mezzanine.pages.models.RichTextPage model which simply contains a WYSIWYG editable field for managing content.

Creating Custom Content Types

In order to handle different types of pages that require more structured content than provided by the RichTextPage model, you can simply create your own models that inherit from Page. For example if we wanted to have pages that were photo galleries:

from django.db import models
from mezzanine.pages.models import Page

# The members of Page will be inherited by the Gallery model, such as
# title, slug, etc. In this example the Gallery model is essentially a
# container for GalleryImage instances.
class Gallery(Page):
    notes = models.TextField("Notes")

class GalleryImage(models.Model):
    gallery = models.ForeignKey("Gallery")
    image = models.ImageField(upload_to="galleries")

Next you'll need to register your model with Django's admin to make it available as a content type. If your content type only exposes some new fields that you'd like to make editable in the admin, you can simply register your model using the mezzanine.pages.admin.PageAdmin class:

from django.contrib import admin
from mezzanine.pages.admin import PageAdmin
from models import Gallery

admin.site.register(Gallery, PageAdmin)

Any regular model fields on your content type will be available when adding or changing an instance of it in the admin. This is similar to Django's behaviour when registering models in the admin without using an admin class, or when using an admin class without fieldsets defined. In these cases all the fields on the model are available in the admin.

If however you need to customize your admin class, you can inherit from PageAdmin and implement your own admin class. The only difference is that you'll need to take a copy of PageAdmin.fieldsets and modify it if you want to implement your own fieldsets, otherwise you'll lose the fields that the Page model implements:

from copy import deepcopy
from django.contrib import admin
from mezzanine.pages.admin import PageAdmin
from models import Gallery, GalleryImage

gallery_extra_fieldsets = ((None, {"fields": ("notes",)}),)

class GalleryImageInline(admin.TabularInline):
    model = GalleryImage

class GalleryAdmin(PageAdmin):
    inlines = (GalleryImageInline,)
    fieldsets = deepcopy(PageAdmin.fieldsets) + gallery_extra_fieldsets

admin.site.register(Gallery, GalleryAdmin)

When registering content type models with PageAdmin or subclasses of it, the admin class won't be listed in the admin index page, instead being made available as a type of Page when creating new pages from the navigation tree.

Note

When creating custom content types, you must inherit directly from the Page model. Further levels of subclassing are currently not supported. Therefore you cannot subclass the RichTextPage or any other custom content types you create yourself. Should you need to implement a WYSIWYG editable field in the way the RichTextPage model does, you can simply subclass both Page and RichText, the latter being imported from mezzanine.core.models.

Page Permissions

The navigation tree in the admin where pages are managed will take into account any permissions defined using Django's permission system. For example if a logged in user doesn't have permission to add new instances of the Gallery model from our previous example, it won't be listed in the types of pages that user can add when viewing the navigation tree in the admin.

In conjunction with Django's permission system, the Page model also implements the methods can_add, can_change and can_delete. These methods provide a way for custom page types to implement their own permissions by being overridden on subclasses of the Page model.

Each of these methods takes a single argument which is the current request object. This provides the ability to define custom permission methods with access to the current user as well.

Note

The can_add permission in the context of an existing page has a different meaning than in the context of an overall model as is the case with Django's permission system. In the case of a page instance, can_add refers to the ability to add child pages.

For example, if our Gallery content type should only contain one child page at most, and only be deletable when added as a child page (unless you're a superuser), the following permission methodss could be implemented:

class Gallery(Page):
    notes = models.TextField("Notes")

    def can_add(self, request):
        return self.children.count() == 0

    def can_delete(self, request):
        return request.user.is_superuser or self.parent is not None

Displaying Custom Content Types

When creating models that inherit from the Page model, multi-table inheritance is used under the hood. This means that when dealing with the page object, an attribute is created from the subclass model's name. So given a Page instance using the previous example, accessing the Gallery instance would be as follows:

>>> Gallery.objects.create(title="My gallery")
<Gallery: My gallery>
>>> page = Page.objects.get(title="My gallery")
>>> page.gallery
<Gallery: My gallery>

And in a template:

<h1>{{ page.gallery.title }}</h1>
<p>{{ page.gallery.notes }}</p>
{% for galleryimage in page.gallery.galleryimage_set.all %}
<img src="{{ MEDIA_URL }}{{ galleryimage.image }}" />
{% endfor %}

The Page model also contains the method Page.get_content_model for retrieving the custom instance without knowing its type beforehand:

>>> page.get_content_model()
<Gallery: My gallery>

Page Templates

The view function mezzanine.pages.views.page handles returning a Page instance to a template. By default the template pages/page.html is used, but if a custom template exists it will be used instead. The check for a custom template will first check for a template with the same name as the Page instance's slug, and if not then a template with a name derived from the subclass model's name is checked for. So given the above example the templates pages/my-gallery.html and pages/gallery.html would be checked for respectively.

Page Processors

So far we've covered how to create and display custom types of pages, but what if we want to extend them further with more advanced features? For example adding a form to the page and handling when a user submits the form. This type of logic would typically go into a view function, but since every Page instance is handled via the view function mezzanine.pages.views.page we can't create our own views for pages. Mezzanine solves this problem using Page Processors.

Page Processors are simply functions that can be associated to any custom Page models and are then called inside the mezzanine.pages.views.page view when viewing the associated Page instance. A Page Processor will always be passed two arguments - the request and the Page instance, and can either return a dictionary that will be added to the template context, or it can return any of Django's HttpResponse classes which will override the mezzanine.pages.views.page view entirely.

To associate a Page Processor to a custom Page model you must create the function for it in a module called page_processors.py inside one of your INSTALLED_APPS and decorate it using the decorator mezzanine.pages.page_processors.processor_for.

Continuing on from our gallery example, suppose we want to add an enquiry form to each gallery page. Our page_processors.py module in the gallery app would be as follows:

from django import forms
from django.http import HttpResponseRedirect
from mezzanine.pages.page_processors import processor_for
from models import Gallery

class GalleryForm(forms.Form):
    name = forms.CharField()
    email = forms.EmailField()

@processor_for(Gallery)
def gallery_form(request, page):
    form = GalleryForm()
    if request.method == "POST":
        form = GalleryForm(request.POST)
        if form.is_valid():
            # Form processing goes here.
            redirect = request.path + "?submitted=true"
            return HttpResponseRedirect(redirect)
    return {"form": form}

The processor_for decorator can also be given a slug argument rather than a Page subclass. In this case the Page Processor will be run when the exact slug matches the page being viewed.

Non-Page Content

Sometimes you might need to use regular Django applications within your site, that fall outside of Mezzanine's page structure. Mezzanine fully supports using regular Django applications. All you need to do is add the app's urlpatterns to your project's urls.py module. Mezzanine's blog application for example, does not use Page content types, and is just a regular Django app.

Mezzanine provides some helpers for your Django apps to integrate more closely with Mezzanine.

The Displayable Model

The abstract model mezzanine.core.models.Displayable and associated manager mezzanine.core.managers.PublishedManager provide common features for items that can be displayed on the site with their own URLs (also known as slugs). Mezzanine's Page model subclasses it. Some of its features are:

  • Meta data such as a title, description and keywords.
  • Auto-generated slug from the title.
  • Draft/published status with the ability to preview drafts.
  • Pre-dated publishing.
  • Searchable by Mezzanine's :doc:`search-engine`.

Models that do not inherit from the Page model described earlier should subclass the Displayable model if any of the above features are required. An example of this can be found in the mezzanine.blog application, where BlogPost instances contain their own URLs and views that fall outside of the regular URL/view structure of the Page model.

Navigation Integration

A common requirement when using regular Django apps with Mezzanine is for pages in the site's navigation to point to the urlpatterns for the app. Implementing this simply requires creating a page with a URL used by the application.

First create a page via the page tree in the admin, and enter the correct URL (under the Meta data section) that maps to the urlpattern in your Django app. This page will then be marked as protected, which means it can't be deleted via the admin, nor can its URL be changed in the admin, since it points to a separate Django app.

The second optional step, is to wrap the application's views in the mezzanine.pages.decorators.for_page decorator. This will add the page instance to the context variable named page, so the title, description, and any specific fields for the content type that you chose to use when creating the page, will be available in the template that gets loaded. The for_page decorator takes a single argument, the URL for the page that the view should include. For example, here's the start of the view that lists blog posts in Mezzanine's blog application:

from mezzanine.pages.decorators import for_page

@for_page(settings.BLOG_SLUG)
def blog_post_list(request, tag=None, year=None, month=None, username=None,
                   category=None, template="blog/blog_post_list.html"):
    # Regular Django view code from this point on.