Fix for running after on a filter with a relation that is none

Author: Stefan Majoor

binder/views.py

@@ -1561,6 +1561,21 @@ def _after_expr(self, request, after_id, include_annotations):
 		whens = []
 
 		for field in ordering:
+			# Fields are generally strings, except in some edge case, where it is an OrderBy expression.
+			# In thase case, we need to change it back to starting (sigh) for compatability reasons
+
+			if type(field) is not str:
+				_field = field
+
+				field = field.expression.name
+
+				if _field.descending:
+					field = f'-{field}'
+				if _field.nulls_first:
+					field = f'{field}__nulls_first'
+				if _field.nulls_last:
+					field = f'{field}__nulls_last'
+
 			# First we have to split of a leading '-' as indicating reverse
 			reverse = field.startswith('-')
 			if reverse:
@@ -1583,7 +1598,7 @@ def _after_expr(self, request, after_id, include_annotations):
 			# Then we determine what the value is for the obj we need to be after
 			value = obj
 			for attr in field.split('__'):
-				value = getattr(value, attr)
+				value = getattr(value, attr, None)
 			if isinstance(value, models.Model):
 				value = value.pk
 

tests/test_after.py

@@ -88,3 +88,27 @@ def test_ordered_with_null_reversed(self):
 			self.assertEqual(self.get('-birth_date'), 'edbacf')
 			self.assertEqual(self.get('-birth_date', after='c'), 'f')
 			self.assertEqual(self.get('-birth_date', after='b'), 'acf')
+
+	def test_after_with_nullable_foreign_key(self):
+		"""
+		There was a bug that if you filtered on a nullable relation, and the relation was not set for the after,
+		then it would crash. Here we test that this doesn't happen again
+		"""
+
+		first_animal = Animal.objects.all()[0]
+		first_animal.zoo = None
+		first_animal.save()
+
+		self.get('-zoo.name', after=self.mapping[first_animal.pk])
+
+	def test_after_with_nullable_foreign_key_and_nulls_first(self):
+		"""
+		There was a bug that if you filtered on a nullable relation, and the relation was not set for the after,
+		then it would crash. Here we test that this doesn't happen again
+		"""
+
+		first_animal = Animal.objects.all()[0]
+		first_animal.zoo = None
+		first_animal.save()
+
+		self.get('-zoo.name__nulls_first', after=self.mapping[first_animal.pk])