keturn · April 21, 2022 15:21 · May 22, 2017 · May 22, 2017 · May 22, 2017
diff --git a/test_cursorpagination.py b/test_cursorpagination.py
@@ -8,9 +8,8 @@ class FloatyModel(models.Model):
 
 
 class FloatyViewSet(viewsets.ReadOnlyModelViewSet):
-    queryset = FloatyModel.objects.all()
+    queryset = FloatyModel.objects.all().order_by('-score')
     pagination_class = CursorPagination
-    ordering = '-score'
     page_size = 3
 
 

diff --git a/fpcursorpagination.py b/fpcursorpagination.py
@@ -0,0 +1,21 @@
+class FloatingPointCursorPagination(CursorPagination):
+    __rounding_down = decimal.Context(prec=14, rounding=decimal.ROUND_FLOOR)
+    __rounding_up = decimal.Context(prec=14, rounding=decimal.ROUND_CEILING)
+
+    def _get_position_from_instance(self, instance, ordering):
+        field_name = ordering[0].lstrip('-')
+        if isinstance(instance, dict):
+            attr = instance[field_name]
+        else:
+            attr = getattr(instance, field_name)
+
+        if isinstance(attr, float):
+            # repr gives more precision than str
+            # but we still lost some precision just from the postgresql-to-python translation.
+            if ordering[0][0] == '-':
+                attr = self.__rounding_down.create_decimal_from_float(attr)
+            else:
+                attr = self.__rounding_up.create_decimal_from_float(attr)
+
+        attr_str = force_text(attr)
+        return attr_str
diff --git a/test_cursorpagination.py b/test_cursorpagination.py
@@ -0,0 +1,32 @@
+from django.db import models
+from rest_framework import viewsets
+from rest_framework.pagination import CursorPagination
+
+
+class FloatyModel(models.Model):
+    score = models.FloatField()
+
+
+class FloatyViewSet(viewsets.ReadOnlyModelViewSet):
+    queryset = FloatyModel.objects.all()
+    pagination_class = CursorPagination
+    ordering = '-score'
+    page_size = 3
+
+
+class TestFloatingPointCursorPagination(APITestCase):
+    def test_page_boundary_does_not_repeat_elements(self, test_data):
+        for i in range(12):
+            FloatyModel.objects.create(score=i/9.0)
+
+        viewset_url = 'FIXME'
+        first_response = self.client.get(viewset_url)
+
+        first_page_last_item = first_response.data['results'][-1]
+
+        second_response = self.client.get(first_response['next'])
+
+        second_page_first_item = second_response.data['results'][0]
+
+        self.assertNotEqual(first_page_last_item['pk'], second_page_first_item['pk'])
+        self.assertGreater(first_page_last_item['score'], second_page_first_item['score'])