No One Is Perfect

Last year I blogged about a neat trick in Django to have multiple views per HTTP verb. Since then I’ve been playing with RESTful applications and decided to see if there was a nicer way to expose “resources” in Django. The following is what I’ve come up with so far.

Listing: router.py

from django.http import Http404, HttpResponseNotAllowed

def get_handler_method(request_handler, http_method):
    try:
        handler_method = getattr(request_handler, http_method.lower())
        if callable(handler_method):
            return handler_method
    except AttributeError:
        pass

class Resource:

    http_methods = ['GET', 'POST', 'HEAD', 'PUT', 'DELETE', 'OPTIONS', 'TRACE']

    @classmethod
    def dispatch(cls, request, *args, **kwargs):
        request_handler = cls()

        if request.method in cls.http_methods:
            handler_method = get_handler_method(request_handler, request.method)
            if handler_method:
                return handler_method(request, *args, **kwargs)

        methods = [method for method in cls.http_methods if get_handler_method(request_handler, method)]
        if len(methods) > 0:
            return HttpResponseNotAllowed(methods)
        else:
            raise Http404

Listing: views.py

from django.shortcuts import render_to_response, get_object_or_404
from django.http import HttpResponseRedirect
from django.core.urlresolvers import reverse
from router import Resource
from models import Document
from django import forms
import identity

class DocumentForm(forms.Form):
    one = forms.CharField()
    two = forms.CharField()
    date = forms.CharField()

def index(request):
    document_links = []
    for document in Document.objects.all():
        url = reverse('document', args=[document.id])
        document_links.append({ 'identity': document.id, 'url': url })

    new_form_url = reverse('document', args=[identity.NEW])
    model = { 'document_links': document_links, 'new_form_url': new_form_url }
    return render_to_response('index.html', model)

def success(request, document_id):
    document = get_object_or_404(Document, pk=document_id)
    form = DocumentForm(document.get_values())
    form.is_valid()

    model = { 'form': form.cleaned_data, 'index_url': reverse('index') }
    return render_to_response('success.html', model)

class DocumentView(Resource):

    def get(self, request, document_id):
        if identity.is_new(document_id):
            form = DocumentForm()
        else:
            document = get_object_or_404(Document, pk=document_id)
            form = DocumentForm(document.get_values())

        model = { 'form': form, 'index_url': reverse('index') }
        return render_to_response('form.html', model)

    def post(self, request, document_id):
        if identity.is_new(document_id):
            document = Document()
        else:
            document = get_object_or_404(Document, pk=document_id)

        document.set_values(request.POST)
        document.save()

        form = DocumentForm(document.get_values())
        if form.is_valid():
            url = reverse('success', args=[document.id])
        else:
            url = reverse('document', args=[document.id])

        return HttpResponseRedirect(url)

Listing: urls.py

from django.conf.urls.defaults import *
from django.conf import settings
import os, views

urlpatterns = patterns('',
    url(r'^document/(?P<document_id>[A-Za-z0-9\-]+)/$', views.DocumentView.dispatch, name='document'),
    url(r'^success/(?P<document_id>[A-Za-z0-9\-]+)/$', views.success, name='success'),
    url(r'^$', views.index, name='index'),
)

if settings.DEBUG:
    urlpatterns += patterns('',
        (r'^static/(?P<path>.*)$', 'django.views.static.serve',
            {'document_root': os.path.join(os.path.dirname(__file__), 'static')}),
    )

It does add a little bit more magic to the views (since you don’t actually see the dispatch method at all) but it benefits from simpler mapping in urls.py, as well as an easier way to figure out what instance method on a Resource subclass gets called for each HTTP verb. Never felt that comfortable with popping-off of kwargs in last year’s post.