Fix error handling for unsupported lookups

Author: NoahStapp

django_mongodb_backend/gis/lookups.py

@@ -1,12 +1,16 @@
 from django.contrib.gis.db.models.lookups import DistanceLookupFromFunction, GISLookup
+from django.db import NotSupportedError
 
 from django_mongodb_backend.query_utils import process_lhs, process_rhs
 
 
 def _gis_lookup(self, compiler, connection, as_expr=False):
     lhs_mql = process_lhs(self, compiler, connection, as_expr=as_expr)
     rhs_mql = process_rhs(self, compiler, connection, as_expr=as_expr)
-    rhs_op = self.get_rhs_op(connection, rhs_mql)
+    try:
+        rhs_op = self.get_rhs_op(connection, rhs_mql)
+    except KeyError:
+        raise NotSupportedError(f"MongoDB does not support the '{self.lookup_name}' lookup.")
     return rhs_op.as_mql(lhs_mql, rhs_mql, self.rhs_params)
 
 

tests/gis_tests_/tests.py

@@ -8,6 +8,6 @@
 @skipUnlessDBFeature("gis_enabled")
 class LookupTests(TestCase):
     def test_unsupported_lookups(self):
-        msg = "MongoDB does not support the same_as lookup."
+        msg = "MongoDB does not support the 'same_as' lookup."
         with self.assertRaisesMessage(NotSupportedError, msg):
             City.objects.get(point__same_as=Point(95, 30))