Added support to fetch latest object from mongoengine queryset

Update tests

Handle comment to address the incosistent behaviour

Author: Arpit

mongoengine/queryset/base.py

@@ -298,6 +298,23 @@ def first(self):
             result = None
         return result
 
+    def last(self):
+        """Retrieve the latest object matching the query."""
+        if not self._ordering:
+            raise OperationError(
+                "Cannot use `last()` without ordering. Use `order_by()` on the queryset first."
+            )
+
+        queryset = self.clone()
+        if self._none or self._empty:
+            return None
+
+        try:
+            result = queryset[self.count() - 1]
+        except IndexError:
+            result = None
+        return result
+
     def insert(
         self, doc_or_docs, load_bulk=True, write_concern=None, signal_kwargs=None
     ):

tests/queryset/test_queryset.py

@@ -2599,6 +2599,32 @@ def test_order_by(self):
         ages = [p.age for p in self.Person.objects.order_by("")]
         assert ages == [40, 20, 30]
 
+    def test_last(self):
+        """Ensure the retrieval of the latest object from the QuerySet based on the specified ordering."""
+        person1 = self.Person(name="User B", age=40).save()
+        person2 = self.Person(name="User A", age=20).save()
+        person3 = self.Person(name="User C", age=30).save()
+
+        assert self.Person.objects.order_by("age").last() == person1
+        assert self.Person.objects.order_by("-age").last() == person2
+
+        person2.age = 31
+        person2.save()
+        assert self.Person.objects.order_by("-age").last() == person3
+        assert self.Person.objects.order_by("age").last() == person1
+
+        person1.age = 41
+        person1.save()
+        assert self.Person.objects.order_by("age").last() == person1
+
+        assert self.Person.objects.order_by("name").last() == person3
+
+        assert self.Person.objects.filter(age__lt=40).order_by("age").last() == person2
+        assert self.Person.objects.filter(age__gt=50).order_by("age").last() is None
+
+        with pytest.raises(OperationError):
+            self.Person.objects.last()
+
     def test_order_by_optional(self):
         class BlogPost(Document):
             title = StringField()