89 lines
3.1 KiB
Python
89 lines
3.1 KiB
Python
from copy import copy
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from math import ceil
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class InvalidPage(Exception):
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pass
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class ObjectPaginator:
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"""
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This class makes pagination easy. Feed it a QuerySet, plus the number of
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objects you want on each page. Then read the hits and pages properties to
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see how many pages it involves. Call get_page with a page number (starting
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at 0) to get back a list of objects for that page.
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Finally, check if a page number has a next/prev page using
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has_next_page(page_number) and has_previous_page(page_number).
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"""
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def __init__(self, query_set, num_per_page):
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self.query_set = query_set
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self.num_per_page = num_per_page
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self._hits, self._pages = None, None
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self._has_next = {} # Caches page_number -> has_next_boolean
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def get_page(self, page_number):
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try:
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page_number = int(page_number)
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except ValueError:
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raise InvalidPage
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if page_number < 0:
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raise InvalidPage
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# Retrieve one extra record, and check for the existence of that extra
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# record to determine whether there's a next page.
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limit = self.num_per_page + 1
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offset = page_number * self.num_per_page
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object_list = list(self.query_set[offset:offset+limit])
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if not object_list:
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raise InvalidPage
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self._has_next[page_number] = (len(object_list) > self.num_per_page)
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return object_list[:self.num_per_page]
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def has_next_page(self, page_number):
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"Does page $page_number have a 'next' page?"
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if not self._has_next.has_key(page_number):
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if self._pages is None:
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offset = (page_number + 1) * self.num_per_page
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self._has_next[page_number] = len(self.query_set[offset:offset+1]) > 0
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else:
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self._has_next[page_number] = page_number < (self.pages - 1)
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return self._has_next[page_number]
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def has_previous_page(self, page_number):
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return page_number > 0
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def first_on_page(self, page_number):
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"""
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Returns the 1-based index of the first object on the given page,
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relative to total objects found (hits).
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"""
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if page_number == 0:
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return 1
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return (self.num_per_page * page_number) + 1
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def last_on_page(self, page_number):
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"""
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Returns the 1-based index of the last object on the given page,
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relative to total objects found (hits).
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"""
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if page_number == 0 and self.num_per_page >= self._hits:
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return self._hits
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elif page_number == (self._pages - 1) and (page_number + 1) * self.num_per_page > self._hits:
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return self._hits
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return (page_number + 1) * self.num_per_page
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def _get_hits(self):
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if self._hits is None:
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self._hits = self.query_set.count()
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return self._hits
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def _get_pages(self):
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if self._pages is None:
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self._pages = int(ceil(self.hits / float(self.num_per_page)))
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return self._pages
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hits = property(_get_hits)
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pages = property(_get_pages)
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