Placing business logic in serializers

[Lu Ali]

Hello,

just started using this framework and I have a requirement, whereby some logic is required in the serializer to check whether an update can proceed or not.

My view is 
===========================================
class UserUpdate(generics.UpdateAPIView):

    permission_classes = (UserUpdatePermission,)
    serializer_class = UserSerializer


Serializer
===========================================
class UserUpdateSerializer(serializers.ModelSerializer):

    class Meta:
        model = User

    # some function here that checks if can be updated or not.
     def ..


what function to override?
Thanks
Lu