Add support for page_size parameter in CursorPaginator class

rest_framework/pagination.py

@@ -482,6 +482,15 @@ class CursorPagination(BasePagination):
     ordering = '-created'
     template = 'rest_framework/pagination/previous_and_next.html'
 
+    # Client can control the page size using this query parameter.
+    # Default is 'None'. Set to eg 'page_size' to enable usage.
+    page_size_query_param = None
+    page_size_query_description = _('Number of results to return per page.')
+
+    # Set to an integer to limit the maximum page size the client may request.
+    # Only relevant if 'page_size_query_param' has also been set.
+    max_page_size = None
+
     # The offset in the cursor is used in situations where we have a
     # nearly-unique index. (Eg millisecond precision creation timestamps)
     # We guard against malicious users attempting to cause expensive database
@@ -566,6 +575,16 @@ def paginate_queryset(self, queryset, request, view=None):
         return self.page
 
     def get_page_size(self, request):
+        if self.page_size_query_param:
+            try:
+                return _positive_int(
+                    request.query_params[self.page_size_query_param],
+                    strict=True,
+                    cutoff=self.max_page_size
+                )
+            except (KeyError, ValueError):
+                pass
+
         return self.page_size
 
     def get_next_link(self):
@@ -779,7 +798,7 @@ def to_html(self):
     def get_schema_fields(self, view):
         assert coreapi is not None, 'coreapi must be installed to use `get_schema_fields()`'
         assert coreschema is not None, 'coreschema must be installed to use `get_schema_fields()`'
-        return [
+        fields = [
             coreapi.Field(
                 name=self.cursor_query_param,
                 required=False,
@@ -790,3 +809,16 @@ def get_schema_fields(self, view):
                 )
             )
         ]
+        if self.page_size_query_param is not None:
+            fields.append(
+                coreapi.Field(
+                    name=self.page_size_query_param,
+                    required=False,
+                    location='query',
+                    schema=coreschema.Integer(
+                        title='Page size',
+                        description=force_text(self.page_size_query_description)
+                    )
+                )
+            )
+        return fields

tests/test_pagination.py

@@ -633,6 +633,164 @@ def test_cursor_pagination(self):
 
         assert isinstance(self.pagination.to_html(), type(''))
 
+    def test_cursor_pagination_with_page_size(self):
+        (previous, current, next, previous_url, next_url) = self.get_pages('/?page_size=20')
+
+        assert previous is None
+        assert current == [1, 1, 1, 1, 1, 1, 2, 3, 4, 4, 4, 4, 5, 6, 7, 7, 7, 7, 7, 7]
+        assert next == [7, 7, 7, 8, 9, 9, 9, 9, 9, 9]
+
+        (previous, current, next, previous_url, next_url) = self.get_pages(next_url)
+        assert previous == [1, 1, 1, 1, 1, 1, 2, 3, 4, 4, 4, 4, 5, 6, 7, 7, 7, 7, 7, 7]
+        assert current == [7, 7, 7, 8, 9, 9, 9, 9, 9, 9]
+        assert next is None
+
+    def test_cursor_pagination_with_page_size_over_limit(self):
+        (previous, current, next, previous_url, next_url) = self.get_pages('/?page_size=30')
+
+        assert previous is None
+        assert current == [1, 1, 1, 1, 1, 1, 2, 3, 4, 4, 4, 4, 5, 6, 7, 7, 7, 7, 7, 7]
+        assert next == [7, 7, 7, 8, 9, 9, 9, 9, 9, 9]
+
+        (previous, current, next, previous_url, next_url) = self.get_pages(next_url)
+        assert previous == [1, 1, 1, 1, 1, 1, 2, 3, 4, 4, 4, 4, 5, 6, 7, 7, 7, 7, 7, 7]
+        assert current == [7, 7, 7, 8, 9, 9, 9, 9, 9, 9]
+        assert next is None
+
+    def test_cursor_pagination_with_page_size_zero(self):
+        (previous, current, next, previous_url, next_url) = self.get_pages('/?page_size=0')
+
+        assert previous is None
+        assert current == [1, 1, 1, 1, 1]
+        assert next == [1, 2, 3, 4, 4]
+
+        (previous, current, next, previous_url, next_url) = self.get_pages(next_url)
+
+        assert previous == [1, 1, 1, 1, 1]
+        assert current == [1, 2, 3, 4, 4]
+        assert next == [4, 4, 5, 6, 7]
+
+        (previous, current, next, previous_url, next_url) = self.get_pages(next_url)
+
+        assert previous == [1, 2, 3, 4, 4]
+        assert current == [4, 4, 5, 6, 7]
+        assert next == [7, 7, 7, 7, 7]
+
+        (previous, current, next, previous_url, next_url) = self.get_pages(next_url)
+
+        assert previous == [4, 4, 4, 5, 6]  # Paging artifact
+        assert current == [7, 7, 7, 7, 7]
+        assert next == [7, 7, 7, 8, 9]
+
+        (previous, current, next, previous_url, next_url) = self.get_pages(next_url)
+
+        assert previous == [7, 7, 7, 7, 7]
+        assert current == [7, 7, 7, 8, 9]
+        assert next == [9, 9, 9, 9, 9]
+
+        (previous, current, next, previous_url, next_url) = self.get_pages(next_url)
+
+        assert previous == [7, 7, 7, 8, 9]
+        assert current == [9, 9, 9, 9, 9]
+        assert next is None
+
+        (previous, current, next, previous_url, next_url) = self.get_pages(previous_url)
+
+        assert previous == [7, 7, 7, 7, 7]
+        assert current == [7, 7, 7, 8, 9]
+        assert next == [9, 9, 9, 9, 9]
+
+        (previous, current, next, previous_url, next_url) = self.get_pages(previous_url)
+
+        assert previous == [4, 4, 5, 6, 7]
+        assert current == [7, 7, 7, 7, 7]
+        assert next == [8, 9, 9, 9, 9]  # Paging artifact
+
+        (previous, current, next, previous_url, next_url) = self.get_pages(previous_url)
+
+        assert previous == [1, 2, 3, 4, 4]
+        assert current == [4, 4, 5, 6, 7]
+        assert next == [7, 7, 7, 7, 7]
+
+        (previous, current, next, previous_url, next_url) = self.get_pages(previous_url)
+
+        assert previous == [1, 1, 1, 1, 1]
+        assert current == [1, 2, 3, 4, 4]
+        assert next == [4, 4, 5, 6, 7]
+
+        (previous, current, next, previous_url, next_url) = self.get_pages(previous_url)
+
+        assert previous is None
+        assert current == [1, 1, 1, 1, 1]
+        assert next == [1, 2, 3, 4, 4]
+
+    def test_cursor_pagination_with_page_size_negative(self):
+        (previous, current, next, previous_url, next_url) = self.get_pages('/?page_size=-5')
+
+        assert previous is None
+        assert current == [1, 1, 1, 1, 1]
+        assert next == [1, 2, 3, 4, 4]
+
+        (previous, current, next, previous_url, next_url) = self.get_pages(next_url)
+
+        assert previous == [1, 1, 1, 1, 1]
+        assert current == [1, 2, 3, 4, 4]
+        assert next == [4, 4, 5, 6, 7]
+
+        (previous, current, next, previous_url, next_url) = self.get_pages(next_url)
+
+        assert previous == [1, 2, 3, 4, 4]
+        assert current == [4, 4, 5, 6, 7]
+        assert next == [7, 7, 7, 7, 7]
+
+        (previous, current, next, previous_url, next_url) = self.get_pages(next_url)
+
+        assert previous == [4, 4, 4, 5, 6]  # Paging artifact
+        assert current == [7, 7, 7, 7, 7]
+        assert next == [7, 7, 7, 8, 9]
+
+        (previous, current, next, previous_url, next_url) = self.get_pages(next_url)
+
+        assert previous == [7, 7, 7, 7, 7]
+        assert current == [7, 7, 7, 8, 9]
+        assert next == [9, 9, 9, 9, 9]
+
+        (previous, current, next, previous_url, next_url) = self.get_pages(next_url)
+
+        assert previous == [7, 7, 7, 8, 9]
+        assert current == [9, 9, 9, 9, 9]
+        assert next is None
+
+        (previous, current, next, previous_url, next_url) = self.get_pages(previous_url)
+
+        assert previous == [7, 7, 7, 7, 7]
+        assert current == [7, 7, 7, 8, 9]
+        assert next == [9, 9, 9, 9, 9]
+
+        (previous, current, next, previous_url, next_url) = self.get_pages(previous_url)
+
+        assert previous == [4, 4, 5, 6, 7]
+        assert current == [7, 7, 7, 7, 7]
+        assert next == [8, 9, 9, 9, 9]  # Paging artifact
+
+        (previous, current, next, previous_url, next_url) = self.get_pages(previous_url)
+
+        assert previous == [1, 2, 3, 4, 4]
+        assert current == [4, 4, 5, 6, 7]
+        assert next == [7, 7, 7, 7, 7]
+
+        (previous, current, next, previous_url, next_url) = self.get_pages(previous_url)
+
+        assert previous == [1, 1, 1, 1, 1]
+        assert current == [1, 2, 3, 4, 4]
+        assert next == [4, 4, 5, 6, 7]
+
+        (previous, current, next, previous_url, next_url) = self.get_pages(previous_url)
+
+        assert previous is None
+        assert current == [1, 1, 1, 1, 1]
+        assert next == [1, 2, 3, 4, 4]
+
 
 class TestCursorPagination(CursorPaginationTestsMixin):
     """
@@ -671,6 +829,8 @@ def __getitem__(self, sliced):
 
         class ExamplePagination(pagination.CursorPagination):
             page_size = 5
+            page_size_query_param = 'page_size'
+            max_page_size = 20
             ordering = 'created'
 
         self.pagination = ExamplePagination()
@@ -727,6 +887,8 @@ class TestCursorPaginationWithValueQueryset(CursorPaginationTestsMixin, TestCase
     def setUp(self):
         class ExamplePagination(pagination.CursorPagination):
             page_size = 5
+            page_size_query_param = 'page_size'
+            max_page_size = 20
             ordering = 'created'
 
         self.pagination = ExamplePagination()