from django.core.paginator import EmptyPage, Page, PageNotAnInteger, Paginator
from django.utils.translation import gettext as _
[docs]
class LazyPaginator(Paginator):
"""
Implement lazy pagination, preventing any count() queries.
By default, for any valid page, the total number of pages for the paginator will be
- `current + 1` if the number of records fetched for the current page offset is
bigger than the number of records per page.
- `current` if the number of records fetched is less than the number of records per page.
The number of additional records fetched can be adjusted using `look_ahead`, which
defaults to 1 page. If you like to provide a little more extra information on how much
pages follow the current page, you can use a higher value.
.. note::
The number of records fetched for each page is `per_page * look_ahead + 1`, so increasing
the value for `look_ahead` makes the view a bit more expensive.
So::
paginator = LazyPaginator(range(10000), 10)
>>> paginator.page(1).object_list
[1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
>>> paginator.num_pages
2
>>> paginator.page(10).object_list
[91, 92, 93, 94, 95, 96, 97, 98, 99, 100]
>>> paginator.num_pages
11
>>> paginator.page(1000).object_list
[9991, 9992, 9993, 9994, 9995, 9996, 9997, 9998, 9999]
>>> paginator.num_pages
1000
Usage with `~.SingleTableView`::
class UserListView(SingleTableView):
table_class = UserTable
table_data = User.objects.all()
pagination_class = LazyPaginator
Or with `~.RequestConfig`::
RequestConfig(paginate={"paginator_class": LazyPaginator}).configure(table)
.. versionadded :: 2.0.0
"""
look_ahead = 1
def __init__(self, object_list, per_page, look_ahead=None, **kwargs):
self._num_pages = None
self._final_num_pages = None
if look_ahead is not None:
self.look_ahead = look_ahead
super().__init__(object_list, per_page, **kwargs)
def validate_number(self, number):
"""Validate the given 1-based page number."""
try:
if isinstance(number, float) and not number.is_integer():
raise ValueError
number = int(number)
except (TypeError, ValueError):
raise PageNotAnInteger(_("That page number is not an integer"))
if number < 1:
raise EmptyPage(_("That page number is less than 1"))
return number
def page(self, number):
# Number might be None, because the total number of pages is not known in this paginator.
# If an unknown page is requested, serve the first page.
number = self.validate_number(number or 1)
bottom = (number - 1) * self.per_page
top = bottom + self.per_page
# Retrieve more objects to check if there is a next page.
look_ahead_items = (self.look_ahead - 1) * self.per_page + 1
objects = list(self.object_list[bottom : top + self.orphans + look_ahead_items])
objects_count = len(objects)
if objects_count > (self.per_page + self.orphans):
# If another page is found, increase the total number of pages.
self._num_pages = number + (objects_count // self.per_page)
# In any case, return only objects for this page.
objects = objects[: self.per_page]
elif (number != 1) and (objects_count <= self.orphans):
raise EmptyPage(_("That page contains no results"))
else:
# This is the last page.
self._num_pages = number
# For rendering purposes in `table_page_range`, we have to remember the final count
self._final_num_pages = number
return Page(objects, number, self)
def is_last_page(self, number):
return number == self._final_num_pages
def _get_count(self):
raise NotImplementedError
count = property(_get_count)
def _get_num_pages(self):
return self._num_pages
num_pages = property(_get_num_pages)
def _get_page_range(self):
raise NotImplementedError
page_range = property(_get_page_range)