Backstory: On Saturday, November 17, 2012 Audrey Roy and I decided to participate in the Petcentric hackathon, a Los Angeles area Pet-themed product/coding contest held at Amplify. We arrived a bit late, but armed with Audrey’s idea of creating a pet based reference sheet for owners, pet sitters, vets, and anyone else needing a card with data on pets, we got to work. About eight hours later we toggled a DNS switch and petcheatsheets.com was live.
Update: Pet Cheatsheet’s owner’s pet information is private, because it includes emergency contact information that often includes phone numbers, email addresses, and even physical addresses of family members and friends. Maintaining the privacy of pets and their owners was also a consideration in implementation.
URL Design Thoughts
During development, one of the things I considered carefully was URL design of the primary feature, which was pets. The obvious choice was to go with a design that identified owners with pets:
However, upon reflection, this didn’t sit well with me. What if a pet changed owners? Identifying a pet with a particular owner in the URL meant that if we ever added a ‘transfer ownership’ feature, there would be extra work. Also, if we ever implemented a sharing feature, changing URLs on a pet going to the same veterinarian their whole life might make the veterinarian’s list of pets and their URLs invalid.
With that in mind, I decided to go with an identifier and pet name, where the pet name was actually not used in the lookup:
One more thing, rather than just use the pet table’s primary key as <pet_id> I decided to go with base36 (0-9 and a-z) encoding. It’s not unlike what URL shortening services do, and if we gained any traction, it makes recitation of a pet’s URL easier. So the final result was actually:
Here’s a simplified view of the final implementation, starting with the model:
# pets/models.py from django.db import models from django.utils.translation import ugettext_lazy as _ class Pet(models.Model): name = models.CharField(_("Pet's name"), max_length=100) identifier = models.CharField(_("identifier"), max_length=50, null=True, blank=True, db_index=True) # More fields...
Then the form:
# pets/forms.py from django import forms from pets.models import Pet class PetForm(forms.ModelForm): class Meta: model = Pet fields = ('name', ) # more fields
With model and form, we build the views:
# pets/views.py from django.shortcuts import get_object_or_404 from django.utils.baseconv import base36 from django.views.generic import CreateView, DetailView, UpdateView from braces.views import LoginRequiredMixin from pets.forms import PetForm class PetCreateView(LoginRequiredMixin, CreateView): model = Pet form_class = PetForm def form_valid(self, form): pet = form.save() pet.identifier = base36.encode(pet.pk) pet.owner = self.request.user # Save again - it's not taking THAT many server cycles AND we needed # the pet.pk in advance to generate the pet.identifier pet.save() return super(PetCreateView, self).form_valid(form) class GetPetMixin(object): """ Any view that needs to get a Pet object can use this Mixin Pet Cheatsheet's owner's pet information is private, because it includes emergency contact information that often includes phone numbers, email addresses, and even physical addresses of family members and friends. """ def get_object(self): pet = get_object_or_404(Pet, identifier=self.kwargs['identifier']) if pet.owner != self.request.user: # Rather than a 'forbidden' result, we want to show a 'Pet Not # Found' page so we can educate site users. raise Http404 return pet class PetDetailView(LoginRequiredMixin, GetPetMixin, DetailView): pass class PetUpdateView(LoginRequiredMixin, GetPetMixin, UpdateView): model = Pet form_class = PetForm class PetPDFView(LoginRequiredMixin, GetPetMixin, DetailView): model = Pet # snip: lots of code for rendering the PDFs.
Then we wire up the views into the urls:
from django.conf.urls.defaults import patterns, url from pets import views urlpatterns = patterns("", url( regex=r"^build-cheatsheet/$", view=views.PetCreateView.as_view(), name="pet_create", ), url( regex=r"^update/(?P<identifier>[\w\d]+)/(?P<slug>[\w\d\-\_]+)/$", view=views.PetUpdateView.as_view(), name="pet_update", ), url( regex=r"^(?P<identifier>[\w\d]+)/(?P<slug>[\w\d\-\_]+)/$", view=views.PetDetailView.as_view(), name="pet_detail", ), # snip: a lot of other views )
In the image below you can see how Marko’s URL has his own unique identifier, along with his name. I can change the name in the URL or even in the database, but so long as I don’t modify the identifying part of the URL (1m), his information always shows up.