url(r'^categories/(S+)/$',views.ItemListView.as_view(),name = 'Item-list'),

class ItemListView(generics.ListAPIView):
    serializer_class = ItemSerializer
    renderer_classes = (JSONRenderer,BrowsableAPIRenderer)

    def get_queryset(self):
        category = get_object_or_404(Category, pk =self.args[0])
        return Items.objects.filter(category = category)

User-Agent: Mozilla/5.0 (X11; Ubuntu; Linux x86_64; rv:40.0) Gecko/20100101 Firefox/40.0
Origin: http://localhost:8000
Host:   127.0.0.1:8000
Connection: keep-alive
Access-Control-Request-Method:  GET
Access-Control-Request-Headers: content-type
Accept-Language:    en-US,en;q=0.5
Accept-Encoding:    gzip, deflate
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8

$('#category-box-list').on('click',function(){
  console.log('selected');
  var cat = $('#category-box-list').val();
  $.ajax({
    type :'GET',
    url :'http://127.0.0.1:8000/billing/categories/' + cat,
    contentType: 'application/json',
    crossDomain:true,
    success : function(json){
      console.log(json);
    }
  });
});