What's the differences between has_object_permission and has_permission? - django

Question

I am confused with the BasePermission in Django-rest-framework.
Here I defined a class: IsAuthenticatedAndOwner.
class IsAuthenticatedAndOwner(BasePermission):
message = 'You must be the owner of this object.'
def has_permission(self, request, view):
print('called')
return False
def has_object_permission(self, request, view, obj):
# return obj.user == request.user
return False
Using in views.py
class StudentUpdateAPIView(RetrieveUpdateAPIView):
serializer_class = StudentCreateUpdateSerializer
queryset = Student.objects.all()
lookup_field = 'pk'
permissions_classes = [IsAuthenticatedAndOwner]
But it doesn't work at all. Everyone can pass the permission and update the data.
The called wasn't printed.
And I used to define this class: IsNotAuthenticated
class IsNotAuthenticated(BasePermission):
message = 'You are already logged in.'
def has_permission(self, request, view):
return not request.user.is_authenticated()
It works well in the function
class UserCreateAPIView(CreateAPIView):
serializer_class = UserCreateSerializer
queryset = User.objects.all()
permission_classes = [IsNotAuthenticated]
So, what are the differences between the examples above, and function has_object_permission & has_permission?

Answer 1

We have following two permission methods on BasePermission class:
def has_permission(self, request, view)
def has_object_permission(self, request, view, obj)
Those two different methods are called for restricting unauthorized users for data insertion and manipulation.
has_permission is called on all HTTP requests whereas, has_object_permission is called from DRF's method def get_object(self). Hence, has_object_permission method is available for GET, PUT, DELETE, not for POST request.
In summary:
permission_classes are looped over the defined list.
has_object_permission method is called after has_permission method returns value True except in POST method (in POST method only has_permission is executed).
When a False value is returned from the permission_classes method, the request gets no permission and will not loop more, otherwise, it checks all permissions on looping.
has_permission method will be called on all (GET, POST, PUT, DELETE) HTTP request.
has_object_permission method will not be called on HTTP POST request, hence we need to restrict it from has_permission method.

Answer 2

Basically, the first code denies everything because has_permission return False.
has_permission is a check made before calling the has_object_permission. That means that you need to be allowed by has_permission before you get any chance to check the ownership test.
What you want is:
class IsAuthenticatedAndOwner(BasePermission):
message = 'You must be the owner of this object.'
def has_permission(self, request, view):
return request.user and request.user.is_authenticated
def has_object_permission(self, request, view, obj):
return obj.user == request.user
This will also allow authenticated users to create new items or list them.

Answer 3

I think this can help:
class IsAuthorOrReadOnly(permissions.BasePermission):
def has_object_permission(self, request, view, obj):
# Read-only permissions are allowed for any request
if request.method in permissions.SAFE_METHODS:
return True
# Write permissions are only allowed to the author of a post
return obj.user == request.user

Answer 4

has_permission() is a method on the BasePermission class that is used to check if the user has permission to perform a certain action on the entire model. For example, you might use it to check if a user has permission to view a list of all objects of a certain model.
has_object_permission() is a method on the BasePermission class that is used to check if the user has permission to perform a certain action on a specific instance of the model. For example, you might use it to check if a user has permission to view, update or delete a specific object of a certain model.
For example, you might have a Book model and a User model in your application. You could use has_permission() to check if a user has permission to view a list of all books, while you use has_object_permission() to check if a user has permission to view, update or delete a specific book.
class IsBookOwnerOrAdmin(permissions.BasePermission):
def has_permission(self, request, view):
# Check if the user is authenticated
if not request.user.is_authenticated:
return False
# Allow access for superusers
if request.user.is_superuser:
return True
# Allow access if the user is the owner of the book
if request.method in permissions.SAFE_METHODS:
return True
return False
def has_object_permission(self, request, view, obj):
# Allow access for superusers
if request.user.is_superuser:
return True
# Allow access if the user is the owner of the book
return obj.owner == request.user

Answer 5

As far as I can see, you are not adding your custom permission to the class as an argument.
This is your code:
class StudentUpdateAPIView(RetrieveUpdateAPIView):
serializer_class = StudentCreateUpdateSerializer
queryset = Student.objects.all()
lookup_field = 'pk'
permissions_classes = [IsAuthenticatedAndOwner]
But it should be:
class StudentUpdateAPIView(RetrieveUpdateAPIView, IsAuthenticatedAndOwner):
serializer_class = StudentCreateUpdateSerializer
queryset = Student.objects.all()
lookup_field = 'pk'
permissions_classes = [IsAuthenticatedAndOwner]
Note the custom permission IsAuthenticatedAndOwner as an argument in the class header.
PS: I hope this helps, I am a beginner in DRF but this is one of the things I just learned.