How to pass parameters to a mixin on a per-view basis

Question

I have an app for managing test cases, which are organised into various projects. I'm trying to set permissions on a per project basis, ie every user has different permissions for each project. Here's what I've come up with so far:

class TestProjectMember(models.Model):
    """Per project permissions - a role can be set for each user for each project"""
    member_name = models.ForeignKey(User, on_delete=models.SET_NULL)
    project = models.ForeignKey(TestProject, on_delete=models.CASCADE)
    member_role = models.CharField(choices=Choices.roles)

class TestCase(models.Model):
    """Test cases"""
    tc_title = models.CharField(max_length=500, unique=True)
    tc_project = models.ForeignKey(TestProject, on_delete=models.CASCADE)

class TestProject(models.Model):
    """Projects"""
    project_name = models.CharField(max_length=200)
    project_desc = models.CharField(max_length=500)



class TestCaseEditHeader(View):

    def get(self, request, pk):
        case = get_object_or_404(TestCase, id=pk)
        if self.get_perm(case.tc_project, request.user, 'TA'):
            form = TestCaseHeaderForm(instance=case)
            context = {'case': case, 'form': form}
            return render(request, 'test_case/tc_header_edit.html', context)
        else:
            return redirect('case_list')

        def get_perm(self, curr_project, curr_user, perm):
            model_perm = TestProjectMember.objects.filter(member_name=curr_user, 
                project=curr_project).values_list('member_role', flat=True)
            if perm in model_perm:
                return True
            return False

It works, but it's a bit clunky. I'd have to call the get_perm() method from every get() or post() method from each view. A better solution would probably be a mixin. What has me stumped is how to pass the required role to the mixin for each view. For each view there is a required role that the user has to have to be able to use the view for the project the test case belongs to. How do I tell the mixin, which particular role is required for which view?

Answer 1

You can just set it as a class attribute.

Note, your query is pretty inefficient; you should just request the perm you want directly.

class TestPermMixin:
    def get_perm(self, curr_project, curr_user):
        return TestProjectMember.objects.filter(
             member_name=curr_user, project=curr_project, member_role=self.perm
        ).exists()

And then set the attribute in the concrete class:

class TestCaseEditHeader(View):
    perm = 'TA'