Django: How to upgrade this old functional view to new class based view?

urls.py

###### NEW:

from django.conf.urls.defaults import *
from sporty import views

urlpatterns = patterns('',
    
    url(
        # 30 characters or fewer. Letters, numbers and @/./+/-/_ characters:
        r'^users/(?P<username>[a-zA-Z0-9@.+-_]+)/$',
        views.UserDetail.as_view(),
        name='user-detail',
    ),
    
)

urls_old.py

###### OLD:

from django.conf.urls.defaults import *
from django.views.generic.simple import direct_to_template

urlpatterns = patterns('dee.views',
    
    # 30 characters or fewer. Letters, numbers and @/./+/-/_ characters:
    url(r'^users/(?P<username>[a-zA-Z0-9@.+-_]+)/$', 'user_detail', {}, name='user-detail'),
    
)

views.py

###### NEW:

from django import shortcuts
from django.views import generic
from django.contrib.auth.models import User

class UserDetail(generic.DetailView):
    
    context_object_name = 'user'
    template_name='sporty/user_detail.html'
    
    def get_queryset(self):
        
        # ERROR HERE: "Generic detail view UserDetail must be called with either an object pk or a slug."
        user = shortcuts.get_object_or_404(User, username__iexact=self.kwargs['username'])
        # ^
        self.profile = user.get_profile()
        
        return user
    
    def get_context_data(self, **kwargs):
        
        context = super(UserDetail, self).get_context_data(**kwargs)
        
        context['profile'] = self.profile

views_old.py

###### OLD:

from django.shortcuts import render_to_response, get_object_or_404
from django.template import RequestContext
from django.contrib.auth.models import User

def user_detail(request, username, template='dee/user_detail.html'):
    
    user = get_object_or_404(User, username__iexact=username)
    
    profile = user.get_profile()
    
    context = {
        'user': user,
        'profile': profile,
    }
    
    return render_to_response(
        template,
        context,
        RequestContext(request),
    )