Django 5 Release
6th November 2023Grid System in UX design
23rd November 2023This post aims to address the ten most common anti-patterns in Django, a popular Python framework. Make sure to avoid these pitfalls to ensure the production-readiness of your code. No time to waste, let’s get started 🏃♂️
1. Fat Models
Remember, Django’s philosophy is “Fat models, thin views.” However, bloating models with logic is an anti-pattern. Encapsulate the related logic into separate classes or functions.
# Anti-pattern
class Order(models.Model):
...
def total(self):
return sum(i.price for i in self.items.all())
# Better approach
class Order(models.Model):
...
def total(self):
return OrderCalculator(self).total()
class OrderCalculator:
def __init__(self, order):
self.order = order
def total(self):
return sum(i.price for i in self.order.items.all())
2. Using Null=True on String-Based Fields
In Django, empty string values will always be stored as empty strings, not as NULL. Don’t use Null=True for string-based fields like CharField and TextField unless necessary.
# Anti-pattern
name = models.CharField(max_length=100, null=True)
# Better approach
name = models.CharField(max_length=100, default="")
3. Repeating Business Logic in Views and Models
Avoid repeating code — ensure DRY (Don’t Repeat Yourself) principle.
# Anti-pattern
def view(request):
order = get_object_or_404(Order, id=request.POST['order'])
order.status = 'shipped'
order.shipped_date = datetime.datetime.now()
order.save()
# Better approach
def view(request):
order = get_object_or_404(Order, id=request.POST['order'])
order.mark_as_shipped()
4. Direct Database Queries in Templates
Never make direct DB queries in templates; it’s against the MVC pattern and can cause performance issues.
<!-- Anti-pattern -->
{% for item in order.items.all %}
<!-- Better approach -->
<!-- Query done in view -->
{% for item in items %}
5. Not Using Django’s ORM Capabilities
Django ORM offers powerful features, like the F()
expressions, to reduce the number of DB hits and increase efficiency.
# Anti-pattern
product.view_count = product.view_count + 1
product.save()
# Better approach
from django.db.models import F
product.view_count = F('view_count') + 1
product.save(update_fields=['view_count'])
6. Ignoring Django Forms
Avoid handling form logic in views. Django’s forms allow you to encapsulate all form-related logic, including validation.
# Anti-pattern
def register(request):
if request.method == 'POST':
if not request.POST.get('username'):
return HttpResponse("Username is required")
# Better approach
class RegisterForm(forms.Form):
username = forms.CharField()
def register(request):
if request.method == 'POST':
form = RegisterForm(request.POST)
if form.is_valid():
...
7. Not Using Django’s Built-in Decorators
Decorators can make the code cleaner. Use them, particularly for access control.
# Anti-pattern
def edit(request, id):
if not request.user.is_authenticated:
return redirect('login')
...
# Better approach
from django.contrib.auth.decorators import login_required
@login_required
def edit(request, id):
...
8. Hardcoding URLs
Hardcoding URLs can cause problems when changing URL structure. Use Django’s reverse()
function or the `{% url % }` template tag.
# Anti-pattern
def view(request):
return redirect('/home/')
# Better approach
from django.urls import reverse
def view(request):
return redirect(reverse('home'))
In templates:
<!-- Anti-pattern -->
<a href="/home/">Home</a>
<!-- Better approach -->
<a href="{% url 'home' %}">Home</a>
9. Not Optimizing QuerySets
Avoid N+1 problem by using select_related
and prefetch_related
.
# Anti-pattern
for order in Order.objects.all():
print(order.customer.name) # Each iteration hits the DB
# Better approach
for order in Order.objects.select_related('customer').all():
print(order.customer.name) # Hits the DB once
10. Ignoring Django’s Testing Framework
Writing tests is not an option but a requirement. Django’s built-in testing framework is powerful; make the most of it.
# Anti-pattern
# Missing tests!
# Better approach
from django.test import TestCase
from .models import Order
class OrderModelTest(TestCase):
def test_order_total(self):
...
Remember, writing maintainable and efficient Django code is an art that requires constant learning. Keep these anti-patterns in mind to avoid common pitfalls, ensure code quality and enhance the performance of your Django applications.
Fore More Information: xpertlab.com