make less than lookups exclude null values

django_mongodb/base.py

@@ -100,8 +100,10 @@ def _isnull_operator(a, b):
         "exact": lambda a, b: {"$eq": [a, b]},
         "gt": lambda a, b: {"$gt": [a, b]},
         "gte": lambda a, b: {"$gte": [a, b]},
-        "lt": lambda a, b: {"$lt": [a, b]},
-        "lte": lambda a, b: {"$lte": [a, b]},
+        # MongoDB considers null less than zero. Exclude null values to match
+        # SQL behavior.
+        "lt": lambda a, b: {"$and": [{"$lt": [a, b]}, {"$ne": [a, None]}]},
+        "lte": lambda a, b: {"$and": [{"$lte": [a, b]}, {"$ne": [a, None]}]},
         "in": lambda a, b: {"$in": [a, b]},
         "isnull": _isnull_operator,
         "range": lambda a, b: {

django_mongodb/features.py

@@ -62,8 +62,6 @@ class DatabaseFeatures(BaseDatabaseFeatures):
         # the result back to UTC.
         "db_functions.datetime.test_extract_trunc.DateFunctionWithTimeZoneTests.test_trunc_func_with_timezone",
         "db_functions.datetime.test_extract_trunc.DateFunctionWithTimeZoneTests.test_trunc_timezone_applied_before_truncation",
-        # Length of null considered zero rather than null.
-        "db_functions.text.test_length.LengthTests.test_basic",
         # Unexpected alias_refcount in alias_map.
         "queries.tests.Queries1Tests.test_order_by_tables",
         # The $sum aggregation returns 0 instead of None for null.

tests/lookup_/models.py

@@ -0,0 +1,11 @@
+from django.db import models
+
+
+class Number(models.Model):
+    num = models.IntegerField(blank=True, null=True)
+
+    class Meta:
+        ordering = ("num",)
+
+    def __str__(self):
+        return str(self.num)

tests/lookup_/tests.py

@@ -0,0 +1,17 @@
+from django.test import TestCase
+
+from .models import Number
+
+
+class NumericLookupTests(TestCase):
+    @classmethod
+    def setUpTestData(cls):
+        cls.objs = Number.objects.bulk_create(Number(num=x) for x in range(5))
+        # Null values should be excluded in less than queries.
+        Number.objects.create()
+
+    def test_lt(self):
+        self.assertQuerySetEqual(Number.objects.filter(num__lt=3), self.objs[:3])
+
+    def test_lte(self):
+        self.assertQuerySetEqual(Number.objects.filter(num__lte=3), self.objs[:4])