def paginate_resource(request, qs, resource_transformer=lambda x: x,
on_empty_message=None):
"""From a request object (an obj that has a dict-like .GET attribute) and a
query set, returns a properly paginated query set, together with the info
about total pages and current page.
Searches the GET query string for a parameter named "page"
:param request: a request object
:param qs: a queryset (or any - preferably unevaluated - iterable, that
supports slicing)
:param resource_transformer: a callable, able to transform the queryset
model instances into resources (dictionaries usually)
:param on_empty_message: the message to be displayed in case there are no
elements in the query set.
:return: tree structure representing the result
"""
current_page, page_size = get_page_details_for_request(request)
paginator = Paginator(qs, page_size, allow_empty_first_page=False)
try:
page = paginator.page(current_page)
except EmptyPage:
if current_page == 1:
raise Http404Error(on_empty_message)
else:
raise Http400Error("Invalid page number. Minimum is 1, maximum is "
"{}".format(paginator.num_pages))
objects_on_page = page.object_list
result = OrderedDict()
result['collection_info'] = serialize_page_metadata(
page, request.build_absolute_uri())
result['objects'] = resource_transformer(objects_on_page)
result.status_code = 200
return result
