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Fix CursorPagination when objects get deleted between calls (#6504) (#6593)

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* Added regression tests (#6504)

Co-Authored-By: Tom Quinonero <tq@3yourmind.com>

* Fix CursorPagination when objects get deleted between calls (#6504)

Co-Authored-By: Tom Quinonero <tq@3yourmind.com>
This commit is contained in:
Joachim Jablon 2019-05-20 15:41:31 +02:00 committed by Tom Christie
parent ac0f0a1774
commit 43a9cc1b7a
2 changed files with 60 additions and 4 deletions
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18
rest_framework/pagination.py
View File

@ -637,7 +637,7 @@ class CursorPagination(BasePagination):
if not self.has_next:
return None
if self.cursor and self.cursor.reverse and self.cursor.offset != 0:
if self.page and self.cursor and self.cursor.reverse and self.cursor.offset != 0:
# If we're reversing direction and we have an offset cursor
# then we cannot use the first position we find as a marker.
compare = self._get_position_from_instance(self.page[-1], self.ordering)
@ -645,12 +645,14 @@ class CursorPagination(BasePagination):
compare = self.next_position
offset = 0
has_item_with_unique_position = False
for item in reversed(self.page):
position = self._get_position_from_instance(item, self.ordering)
if position != compare:
# The item in this position and the item following it
# have different positions. We can use this position as
# our marker.
has_item_with_unique_position = True
break
# The item in this position has the same position as the item
@ -659,7 +661,7 @@ class CursorPagination(BasePagination):
compare = position
offset += 1
else:
if self.page and not has_item_with_unique_position:
# There were no unique positions in the page.
if not self.has_previous:
# We are on the first page.
@ -678,6 +680,9 @@ class CursorPagination(BasePagination):
offset = self.cursor.offset + self.page_size
position = self.previous_position
if not self.page:
position = self.next_position
cursor = Cursor(offset=offset, reverse=False, position=position)
return self.encode_cursor(cursor)
@ -685,7 +690,7 @@ class CursorPagination(BasePagination):
if not self.has_previous:
return None
if self.cursor and not self.cursor.reverse and self.cursor.offset != 0:
if self.page and self.cursor and not self.cursor.reverse and self.cursor.offset != 0:
# If we're reversing direction and we have an offset cursor
# then we cannot use the first position we find as a marker.
compare = self._get_position_from_instance(self.page[0], self.ordering)
@ -693,12 +698,14 @@ class CursorPagination(BasePagination):
compare = self.previous_position
offset = 0
has_item_with_unique_position = False
for item in self.page:
position = self._get_position_from_instance(item, self.ordering)
if position != compare:
# The item in this position and the item following it
# have different positions. We can use this position as
# our marker.
has_item_with_unique_position = True
break
# The item in this position has the same position as the item
@ -707,7 +714,7 @@ class CursorPagination(BasePagination):
compare = position
offset += 1
else:
if self.page and not has_item_with_unique_position:
# There were no unique positions in the page.
if not self.has_next:
# We are on the final page.
@ -726,6 +733,9 @@ class CursorPagination(BasePagination):
offset = 0
position = self.next_position
if not self.page:
position = self.previous_position
cursor = Cursor(offset=offset, reverse=True, position=position)
return self.encode_cursor(cursor)

46
tests/test_pagination.py
View File

@ -630,6 +630,52 @@ class CursorPaginationTestsMixin:
assert isinstance(self.pagination.to_html(), str)
def test_cursor_pagination_current_page_empty_forward(self):
# Regression test for #6504
self.pagination.base_url = "/"
# We have a cursor on the element at position 100, but this element doesn't exist
# anymore.
cursor = pagination.Cursor(reverse=False, offset=0, position=100)
url = self.pagination.encode_cursor(cursor)
self.pagination.base_url = "/"
# Loading the page with this cursor doesn't crash
(previous, current, next, previous_url, next_url) = self.get_pages(url)
# The previous url doesn't crash either
(previous, current, next, previous_url, next_url) = self.get_pages(previous_url)
# And point to things that are not completely off.
assert previous == [7, 7, 7, 8, 9]
assert current == [9, 9, 9, 9, 9]
assert next == []
assert previous_url is not None
assert next_url is not None
def test_cursor_pagination_current_page_empty_reverse(self):
# Regression test for #6504
self.pagination.base_url = "/"
# We have a cursor on the element at position 100, but this element doesn't exist
# anymore.
cursor = pagination.Cursor(reverse=True, offset=0, position=100)
url = self.pagination.encode_cursor(cursor)
self.pagination.base_url = "/"
# Loading the page with this cursor doesn't crash
(previous, current, next, previous_url, next_url) = self.get_pages(url)
# The previous url doesn't crash either
(previous, current, next, previous_url, next_url) = self.get_pages(next_url)
# And point to things that are not completely off.
assert previous == [7, 7, 7, 7, 8]
assert current == []
assert next is None
assert previous_url is not None
assert next_url is None
def test_cursor_pagination_with_page_size(self):
(previous, current, next, previous_url, next_url) = self.get_pages('/?page_size=20')