Pinax: a platform for rapidly developing websites

posted on May 4th, 2009 by PyromanX in Greg's Bookmarks on Delicious

How to Write Django Template Tags

posted on January 22nd, 2009 by Greg Allard in Greg's Posts on Code Spatter

Template tags can be useful for making your applications more reusable by other projects. For this example I will be adding to the books project that I started in a previous post. Also, I’ve bundled the example files into a google code project.

Start off by creating a folder called templatetags in your app directory and create two files in it. The first one named __init__.py and the second book_tags.py. There’s 3 things that we need to accomplish with our template tags. The first is to create a tag that will output the url for the action of the form. For example, {% get_book_form_url foo_object %}Next we need to get the form and assign it to a template variable that can be specified by the template variable. For example, {% book_form as bar_var %}. And the third template tag will get the books for an object and place in a template variable. For example, {% books_for_object foo_object as bar_var %}.

from django.template import Library, Node, TemplateSyntaxError
from django.template import Variable, resolve_variable
from django.utils.translation import ugettext as _
from django.contrib.contenttypes.models import ContentType
from django.core.urlresolvers import reverse
from books.models import Book
 
register = Library()
 
def get_contenttype_kwargs(content_object):
    """
    Gets the basic kwargs necessary for form submission url
    """
    kwargs = {'content_type_id':
        ContentType.objects.get_for_model(content_object).id,
    'object_id':
        getattr(content_object, 'pk',
            getattr(content_object, 'id')),
    }
    return kwargs
 
def get_book_form_url(content_object):
    """
    prints url for form action
    """
    kwargs = get_contenttype_kwargs(content_object)
    return reverse('new_book', kwargs=kwargs)
 
class BooksForObjectsNode(Node):
    """
    Get the books and add to the context
    """
    def __init__(self, obj, context_var):
        self.obj = Variable(obj)
        self.context_var = context_var
 
    def render(self, context):
        content_type = ContentType.objects.get_for_model(
            self.obj.resolve(context))
        # create the template var by adding to context
        context[self.context_var] = \
            Book.objects.filter( # find all books for object
                content_type__pk = content_type.id,
                object_id = self.obj.resolve(context).id
            )
        return ''
 
def books_for_object(parser, token):
    """
    Retrieves a list of books for given object
    {% books_for_object foo_object as book_list %}
    """
    try:
        bits = token.split_contents()
    except ValueError:
        raise TemplateSyntaxError(
            _('tag requires exactly two arguments')
    if len(bits) != 4:
        raise TemplateSyntaxError(
            _('tag requires exactly three arguments')
    if bits[2] != 'as':
        raise TemplateSyntaxError(
            _("second argument to tag must be 'as'")
    return BooksForObjectsNode(bits[1], bits[3])
 
def book_form(parser, token):
    """
    Adds a form to the context as given variable
    {% book_form as form %}
    """
    # take steps to ensure template var was formatted properly
    try:
        bits = token.split_contents()
    except ValueError:
        raise TemplateSyntaxError(
            _('tag requires exactly two arguments')
    if bits[1] != 'as':
        raise TemplateSyntaxError(
            _("second argument to tag must be 'as'")
    if len(bits) != 3:
        raise TemplateSyntaxError(
            _('tag requires exactly two arguments')
    # get the form
    return BookFormNode(bits[2])
 
class BookFormNode(Node):
    """
    Get the form and add it to the context
    """
    def __init__(self, context_name):
        self.context_name = context_name
    def render(self, context):
        from books.forms import NewBookForm
        form = NewBookForm()
        # create the template var by adding to context
        context[self.context_name] = form
        return ''
 
# register these tags for use in template files
register.tag('books_for_object', books_for_object)
register.tag('book_form', book_form)
register.simple_tag(get_book_form_url)

Add this to your template

To start adding books to an object, add this code to your template and change my_awesome_object_here to the template variable name of your object.

<h2>Books</h2>
{% load book_tags %}
 
{% books_for_object my_awesome_object_here as books %}
{% for book in books %}
 
<a href="{{ book.get_absolute_url }}">{{ book }}</a> -
        {{ book.description }}
 
{% endfor %}
<h2>Add a book</h2>
<form action="{% get_book_form_url my_awesome_object_here %}" method="post">
{% book_form as form %}
{{ form }}
<input type="submit" value="Go" />
</form>

You can get the template tags source code and the code from the previous post at the google code project page or by doing

svn co http://django-books.googlecode.com/svn/trunk books

in a directory on the python path.

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How to Write Reusable Apps for Pinax and Django

posted on January 15th, 2009 by Greg Allard in Greg's Posts on Code Spatter

Pinax is a collection of reusable django apps that brings together features that are common to many websites. It allows developers to focus on what makes their site unique. Here is an example of adding your own functionality to Pinax. It will also be an example of writing a reusable app since every individual app currently in Pinax can be used separately. Also, I’ve bundled the example files into a google code project.

My example will be to create a list of books and allow them to be tied to any object using Django’s ContentType framework. The books could be recommended reading for the members of a tribe (pinax group), a class, or anything in your project and will include title, description, and tags (requires django-tagging). In another post I’ve shown how to create template tags to make it easy to show the list of books and a form to add a book. Obviously, there is a lot more that could be done with this app, but I will leave it out of the example to keep it simple.

Starting the App

Create a folder in the apps directory or any place that is on the python path (ex. /path/to/pinax/projects/complete_project/apps/books/) and include these files:

  • __init__.py even though it might be empty, it is required
  • forms.py
  • models.py
  • urls.py
  • views.py

models.py

I will start with creating the model for the project. Below is all of the code I am placing in the file. I’ve added a lot of comments to explain everything that is happening.

#import all of the things we will be using
from django.db                          import models
from tagging.fields                     import TagField
# to help with translation of field names
from django.utils.translation  import ugettext_lazy as _
# to have a generic foreign key for any model
from django.contrib.contenttypes        import generic
# stores model info so this can be applied to any model
from django.contrib.contenttypes.models import ContentType
 
class Book(models.Model):
    """
    The details of a Book
    """
    # fields that describe this book
    name        = models.CharField(_('name'), max_length=48)
    description = models.TextField(_('description'))
 
    # to add to any model
    content_type   = models.ForeignKey(ContentType)
    object_id      = models.PositiveIntegerField()
    content_object = generic.GenericForeignKey('content_type',
        'object_id')
 
    # for the list of tags for this book
    tags        = TagField()
 
    # misc fields
    deleted     = models.BooleanField(default=0)
    created     = models.DateTimeField(auto_now_add=True)
    # so that {{book.get_absolute_url}} outputs the whole url
    @models.permalink
    def get_absolute_url(self):
        return ("book_details", [self.pk])
    # outputs name when printing this object as a string
    def __unicode__(self):
        return self.name

forms.py

Use Django’s ModelForm to create a form for our book model.

from django import forms
from books.models import Book
 
class NewBookForm(forms.ModelForm):
    class Meta:
        model = Book
        exclude = ('deleted', 'content_type',
            'object_id', 'created')

views.py

In this file we create a view to show the details of a book and a view to create a new book for an object.

from django.shortcuts import render_to_response
from django.shortcuts import get_object_or_404
from django.http import HttpResponseRedirect
from django.template import RequestContext
from django.core.urlresolvers import reverse
from django.utils.translation import ugettext_lazy as _
from django.contrib.auth.decorators import login_required
 
from tribes.models import Tribe
from books.models import Book
from django.contrib.contenttypes.models import ContentType
 
@login_required
def new(request, content_type_id, object_id,
            template_name="books/new.html"):
    """
    creates a new book
    """
    from books.forms import NewBookForm
 
    # if a new book was posted
    if request.method == 'POST':
        book_form = NewBookForm(request.POST)
        if book_form.is_valid():
            # create it
            book = book_form.save(commit=False)
            content_type        = \
                ContentType.objects.get(id=content_type_id)
            content_object      = \
                content_type.get_object_for_this_type(
                id=object_id)
            book.content_object = content_object
            book.save()
            request.user.message_set.create(
                message=
                _("Successfully created book '%s'")
                % book.name)
            # send to object page or book page
            try:
                return HttpResponseRedirect(
                    content_object.get_absolute_url()
                )
            except:
                return HttpResponseRedirect(reverse(
                    'book_details', args=(book.id,)))
        # if invalid, it gets displayed below
    else:
        book_form = NewBookForm()
 
    return render_to_response(template_name, {
        'book_form': book_form,
    }, context_instance=RequestContext(request))
 
@login_required
def details(request, book_id,
    template_name="books/details.html"):
    """
    displays details of a book
    """
    book = get_object_or_404(Book, id=book_id)
    return render_to_response(template_name, {
        'book': book,
    }, context_instance=RequestContext(request))

urls.py

To tie our views to some urls, add this to the urls.py file.

from django.conf.urls.defaults import *
from django.conf.urls.defaults import *
 
urlpatterns = patterns('',    
    # new book for object
    url(r'^new/(?P<content_type_id>\d+)/(?P<object_id>\d+)', 
        'books.views.new', name="new_book"),
    # display details of a book
    url(r'^details/(?P<book_id>\d+)$', 'books.views.details', 
        name="book_details"),
)

More Features

The rest of the application is described in the post titled: How to Write Django Template Tags. You can also check out all of the code from the google project by doing the following command:

svn co http://django-books.googlecode.com/svn/trunk books

in a directory on the python path.

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Django RequestContext Example

posted on December 22nd, 2008 by Greg Allard in Greg's Posts on Code Spatter

Browsing other peoples’ code is a great way to learn new things about a language or framework. I never made it to the Django docs about Contexts, but the Pinax developers apparently did and I got a chance to learn this from them. This is a few sections of their code and how they use RequestContext in their apps.

If you are looking at the source of some of their views you might see how they are using it. Here is what it looks like in friends_app.friends

    return render_to_response(template_name, {
        "join_request_form": join_request_form,
        "invites_received": invites_received,
        "invites_sent": invites_sent,
        "joins_sent": joins_sent,
    }, context_instance=RequestContext(request))

So what extactly does context_instance=RequestContext(request) do? I took a look at the django documentation to find out more. And that led me to check the settings file and I found that there were quite a few things listed in TEMPLATE_CONTEXT_PROCESSORS.

TEMPLATE_CONTEXT_PROCESSORS = (
    "django.core.context_processors.auth",
    "django.core.context_processors.debug",
    "django.core.context_processors.i18n",
    "django.core.context_processors.media",
    "django.core.context_processors.request",
 
    "notification.context_processors.notification",
    "announcements.context_processors.site_wide_announcements",
    "account.context_processors.openid",
    "account.context_processors.account",
    "misc.context_processors.contact_email",
    "misc.context_processors.site_name",
    "messages.context_processors.inbox",
    "friends_app.context_processors.invitations",
    "misc.context_processors.combined_inbox_count",
)

I opened up friends_app.context_processors to see a bit more and it looked like this

from friends.models import FriendshipInvitation
 
def invitations(request):
    if request.user.is_authenticated():
        return {
            'invitations_count':
            FriendshipInvitation.objects.filter(
            to_user=request.user, status="2").count(),
        }
    else:
        return {}

This means that every view that has context_instance=RequestContext(request) in it will call the above function since it is listed in settings.py and it will provide the template variable, {{ invitations_count }}.

Using RequestContext makes it easy to have the common template variables available on every page and I will have to start using it more in my apps. So make sure you have from django.shortcuts import render_to_response and from django.template import RequestContext in your file and add your context processor to the settings file and you should be ready to add template vars to your contexts.

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