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How can I write my own decorator in Django?

My models.py file is as follow:

models.py

from django.contrib.auth.models import User

class Shopkeeper(models.Model):
user = models.OneToOneField(User, on_delete=models.CASCADE, primary_key=True)
# ...


class Customer(models.Model):
user = models.OneToOneField(User, on_delete=models.CASCADE, primary_key=True)
# ...


And I have some views which only Customers can access after login, but Shopkeepers cannot. And vice versa.
How can I write decorator for such task?

1 Answer
1

There is nothing magical about a decorator, it is a function that takes as input the function (or class) to decorate, and makes some changes to it. If we look at the login_required decorator [GitHub], we see:

login_required

def login_required(function=None, redirect_field_name=REDIRECT_FIELD_NAME, login_url=None):
"""
Decorator for views that checks that the user is logged in, redirecting
to the log-in page if necessary.
"""
actual_decorator = user_passes_test(
lambda u: u.is_authenticated,
login_url=login_url,
redirect_field_name=redirect_field_name
)
if function:
return actual_decorator(function)
return actual_decorator


We can thus actually simply make a special case of the user_passes_test decorator:

user_passes_test

from django.contrib.auth.decorators import user_passes_test

def shopkeeper_required(function=None):
def is_shopkeeper(u):
return Shopkeeper.objects.filter(user=u).exists()
actual_decorator = user_passes_test(is_shopkeeper)
if function:
return actual_decorator(function)
else:
return actual_decorator

def customer_required(function=None):
def is_customer(u):
return Customer.objects.filter(user=u).exists()
actual_decorator = user_passes_test(is_customer)
if function:
return actual_decorator(function)
else:
return actual_decorator

You can then for example implement it as:

@login_required
@shopkeeper_required
def some_shopkeeper_view(request):
# ...
pass

@login_required
@customer_required
def some_customer_view(request):
# ...
pass


Note that this @shopkeeper_required does not really enforces that the user is logged in, although in many cases that will be the case.

@shopkeeper_required

EDIT:

We can merge this with a @login_required (by adding a parameter that acts as a switch to turn this behavior on or off, by default on), like:

@login_required

from django.contrib.auth.decorators import user_passes_test

def shopkeeper_required(function=None, login_required=True, redirect_field_name=REDIRECT_FIELD_NAME, login_url=None):
def is_shopkeeper(u):
if login_required and not u.is_authenticated:
return False
return Shopkeeper.objects.filter(user=u).exists()
actual_decorator = user_passes_test(
is_shopkeeper,
login_url=login_url,
redirect_field_name=redirect_field_name
)
if function:
return actual_decorator(function)
else:
return actual_decorator

def customer_required(function=None, login_required=True, redirect_field_name=REDIRECT_FIELD_NAME, login_url=None):
def is_customer(u):
if login_required and not u.is_authenticated:
return False
return Customer.objects.filter(user=u).exists()
actual_decorator = user_passes_test(
is_customer,
login_url=login_url,
redirect_field_name=redirect_field_name
)
if function:
return actual_decorator(function)
else:
return actual_decorator

@login_required

actual_decorator = user_passes_test(u.is_authenticated and is_shopkeeper)

u

u

lambda

user_passes_test(lambda u: u.is_authenticated and is_shopkeeper(u))

'User' object has no attribute 'login_required'

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