Ch 7. Function-and Class-Based Views Ch 8. Best Practices for Function-Based Views

1. Two Scoops of Django
Ch 7. Function-and Class-Based Views
Ch 8. Best Practices for Function-Based Views
2014/11/04
Michelle Leu @flywindy

2. Agenda
Django Views
FBVs v.s. CBVs
Best practices for FBVs
URL Namespaces
Loose Coupling
Summary

3. Django Views
Django Views are functions
y = f(x) # math
HttpResponse = view(HttpRequest) # FBV
HttpResponse = View.as_view(HttpRequest) # CBV

4. Django Views
keep business logic out of Views
model methods
manger methods
general utility helper function
forms
Business logic is the
part of the program
that encodes the real-world
business rules
that determine how
data can be created,
displayed, stored, and
changed…….
(From wikipedia)

5. FBVs (Function Based Views)
Django 1.7 Tutorial Part 3
# polls/views.py
…
from django.shortcuts import render
from polls.models import Question
def index(request):
latest_question_list = Question.objects.all().order_by('-pub_date')[:5]
context = {'latest_question_list': latest_question_list}
return render(request, 'polls/index.html', context)
def detail(request, question_id):
question = get_object_or_404(Question, pk=question_id)
return render(request, 'polls/detail.html', {'question': question})
def results(request, question_id):
question = get_object_or_404(Question, pk=question_id)
return render(request, 'polls/results.html', {'question': question})

6. CBVs (Class Based Views)
Django 1.7 Tutorial Part 4
# polls/views.py
…
from django.views import generic
from polls.models import Question
class IndexView(generic.ListView):
class DetailView(generic.DetailView):
model = Question
template_name = 'polls/detail.html'
class ResultsView(generic.DetailView):
model = Question
template_name = 'polls/results.html'
template_name = 'polls/index.html'
context_object_name = 'latest_question_list'
def get_queryset(self):
"""Return the last five published questions."""
return Question.objects.order_by('-pub_date')[:5]

7. CBVs v.s. FBVs

8. CBVs v.s. FBVs
For new comer: FBVs
For new project: CBVs
For past project: FBVs for most views, CBVs
only for views that need to be subclassed.
Write custom 403, 404, and 500 error handlers:
FBVs # root URLconf
handler500 = 'mysite.views.my_custom_error_view'

9. Best practices for FBVs
Pass HttpRequest Object
Pass HttpResponse Object
Decorators

10. Decorators
simple decorator template
# EXAMPLE 8.5
import functools
def decorator(view_func):
@functools.wraps(view_func)
def new_view_func(request, *args, **kwargs):
# modify HttpRequest object here
response = view_func(request, *args, **kwargs)
# modify HttpResponse object here
return response
return new_view_func

11. Decorators
# EXAMPLE 8.6
# sprinkles/decorators.py
from functools import wraps
from . import utils
def check_sprinkles(view_func):
@wraps(view_func)
def new_view_func(request, *args,
**kwargs):
# modify HttpRequest object here
request =
utils.can_sprinkle(request)
# request.can_sprinkle
response = view_func(request,
*args, **kwargs)
# modify HttpResponse object
here
return response
return new_view_func
# EXAMPLE 8.7
# sprinkles/views.py
...
from .decorators import /
check_sprinkles
@check_sprinkles
def sprinkle_detail(request, pk):
sprinkle =
get_object_or_404(Sprinkle, pk=pk)
return render(request,
"sprinkles/sprinkle_detail.html",
{"sprinkle": sprinkle})

12. URL Namespaces
allow you to uniquely reverse named URL patterns even if different
applications use the same URL names.
are specified using the ':' operator. For example, the main index page of the
admin application is referenced using 'admin:index'. This indicates a
namespace of 'admin', and a named URL of ‘index'.
can also be nested.
# EXAMPLE 7.3
# urls.py at root of project
from django.conf.urls import include, url
urlpatterns += patterns('',
url(r'^tastings/', include('tastings.urls', namespace='tastings')),
)
7.4
tastings/views.py snippet
……
class TasteUpdateView(UpdateView):
model = Tasting
def get_success_url(self):
return reverse("tastings:detail", kwargs={"pk": self.object.pk})

13. URL Namespaces
# EXAMPLE 7.5
# tastings/detail.html snippet
……
<ul>
{% for tasting in tastings %}
<li>
<a href="{% url "tastings:detail" tasting.pk %}">{{ tasting.title }}</a>
<small>
(<a href="{% url "tastings:update" tasting.pk %}">update</a>)
</small>
</li>
{% endfor %}
<ul>
……

14. Why URL Namespaces?
Makes for shorter, more obvious and DRY URL
names
Increases interoperability with Third-party
libraries
Easier searches, upgrades, and refactors
Allow for more app and template reverse tricks

15. Loose Coupling
鬆散耦合
相對於 緊密耦合(tight coupling)
In computing and systems
design a loosely coupled
system is one in which each of
its components has, or makes
use of, little or no knowledge of
the definitions of other separate
components ….…
(From wikipedia)

16. Loose Coupling
# BAD EXAMPLE 7.1
from django.conf.urls import patterns,
url
from django.views.generic import /
DetailView
from tastings.models import Tasting
urlpatterns = patterns('',
url(r'^(?P<pk>d+)/$',
DetailView.as_view(
model=Tasting,
template_name='tastings/
detail.htm'),
name='detail'),
url(r'^(?P<pk>d+)/results/$',
DetailView.as_view(
model=Tasting,
template_name='tastings/
results.html'),
name='results'),
)
authentication︖？

17. Loose Coupling
閃開，讓專業的來！
# EXAMPLE 7.1
# tastings/views.py
from django.views.generic import /
DetailView
from tastings.models import Tasting
class TasteDetailView(DetailView):
model = Tasting
class
TasteResultsView(TasteDetailView):
template_name = 'tastings/
results.html'
# EXAMPLE 7.1
# tastings/urls.py
from django.conf.urls import patterns,
url
from . import views
urlpatterns = patterns('',
url(r'^(?P<pk>d+)/$',
views.TasteDetailView.as_view(),
name='detail'),
url(r'^(?P<pk>d+)/results/$',
views.TasteResultsView.as_view(),
name='results'),
)
<app_label>/<model_name><template_name_suffix>.html -> tastings/tasting_detail.html

18. Summary
Don’t Repeat Yourself. (DRY)
Do one thing and do it well.
Views should handle presentation logic.
Less code is better, and keep it simple.
Complex nested-if blocks are to be avoided.

19. References
Classy Class-Based Views: http://ccbv.co.uk/
Django project 1.7 tutorial: https://docs.djangoproject.com/en/
1.7/intro/tutorial01/
Django project 1.7 - URL namespaces: https://
docs.djangoproject.com/en/1.7/topics/http/urls/#url-namespaces
Django Girls 學習⼿手冊: http://djangogirlstaipei.gitbooks.io/
django-girls-taipei-tutorial/
two-scoops-of-django-1.6 issues: https://github.com/twoscoops/
two-scoops-of-django-1.6/issues?q=is%3Aopen+is%3Aissue