From a2f0f20284ed28c8633ebc6b01a6e9ca71b04f83 Mon Sep 17 00:00:00 2001
From: Matthieu Rigal <matt.rigal@gmail.com>
Date: Thu, 11 Jun 2015 17:48:34 +0200
Subject: [PATCH] Improve error message for invalid query

---
 mongoengine/base/document.py      | 9 +++++++--
 mongoengine/queryset/transform.py | 2 +-
 tests/queryset/transform.py       | 9 +++++++++
 3 files changed, 17 insertions(+), 3 deletions(-)

diff --git a/mongoengine/base/document.py b/mongoengine/base/document.py
index 5707992a..1ab19e75 100644
--- a/mongoengine/base/document.py
+++ b/mongoengine/base/document.py
@@ -983,8 +983,13 @@ class BaseDocument(object):
                 if hasattr(getattr(field, 'field', None), 'lookup_member'):
                     new_field = field.field.lookup_member(field_name)
                 else:
-                   # Look up subfield on the previous field
-                    new_field = field.lookup_member(field_name)
+                    # Look up subfield on the previous field or raise
+                    try:
+                        new_field = field.lookup_member(field_name)
+                    except AttributeError:
+                        raise LookUpError('Cannot resolve subfield or operator {} '
+                                          'on the field {}'.format(
+                                              field_name, field.name))
                 if not new_field and isinstance(field, ComplexBaseField):
                     if hasattr(field.field, 'document_type') and cls._dynamic \
                             and field.field.document_type._dynamic:
diff --git a/mongoengine/queryset/transform.py b/mongoengine/queryset/transform.py
index c43c4b40..f6cfa87e 100644
--- a/mongoengine/queryset/transform.py
+++ b/mongoengine/queryset/transform.py
@@ -44,7 +44,7 @@ def query(_doc_cls=None, _field_operation=False, **query):
         if len(parts) > 1 and parts[-1] in MATCH_OPERATORS:
             op = parts.pop()
 
-        #if user escape field name by __
+        # if user escape field name by __
         if len(parts) > 1 and parts[-1] == "":
             parts.pop()
 
diff --git a/tests/queryset/transform.py b/tests/queryset/transform.py
index 77d3593c..a543317a 100644
--- a/tests/queryset/transform.py
+++ b/tests/queryset/transform.py
@@ -224,6 +224,15 @@ class TransformTest(unittest.TestCase):
         self.assertEqual(1, Doc.objects(item__type__="axe").count())
         self.assertEqual(1, Doc.objects(item__name__="Heroic axe").count())
 
+    def test_understandable_error_raised(self):
+        class Event(Document):
+            title = StringField()
+            location = GeoPointField()
+
+        box = [(35.0, -125.0), (40.0, -100.0)]
+        # I *meant* to execute location__within_box=box
+        events = Event.objects(location__within=box)
+        self.assertRaises(InvalidQueryError, lambda: events.count())
 
 if __name__ == '__main__':
     unittest.main()