Added InvalidDocumentError

Ensures defined documents are valid and users don't override core methods
by accident.

fixes #275

docs/changelog.rst

@@ -5,7 +5,8 @@ Changelog
 Changes in dev
 ==============
 
-- Added GenericEmbeddedDocument - So you can embed any type of embeddable document
+- Added InvalidDocumentError - so Document core methods can't be overwritten
+- Added GenericEmbeddedDocument - so you can embed any type of embeddable document
 - Added within_polygon support - for those with mongodb 1.9
 - Updated sum / average to use map_reduce as db.eval doesn't work in sharded environments
 - Added where() - filter to allowing users to specify query expressions as Javascript

mongoengine/base.py

@@ -16,6 +16,9 @@ class NotRegistered(Exception):
     pass
 
 
+class InvalidDocumentError(Exception):
+    pass
+
 class ValidationError(Exception):
     pass
 
@@ -388,6 +391,8 @@ class DocumentMetaclass(type):
         attrs['_db_field_map'] = dict([(k, v.db_field) for k, v in doc_fields.items() if k!=v.db_field])
         attrs['_reverse_db_field_map'] = dict([(v, k) for k, v in attrs['_db_field_map'].items()])
 
+        from mongoengine import Document
+
         new_class = super_new(cls, name, bases, attrs)
         for field in new_class._fields.values():
             field.owner_document = new_class
@@ -396,6 +401,9 @@ class DocumentMetaclass(type):
                 field.document_type.register_delete_rule(new_class, field.name,
                         delete_rule)
 
+            if field.name and hasattr(Document, field.name):
+                raise InvalidDocumentError("%s is a document method and not a valid field name" % field.name)
+
         module = attrs.get('__module__')
 
         base_excs = tuple(base.DoesNotExist for base in bases

tests/document.py

@@ -12,7 +12,7 @@ import weakref
 from fixtures import Base, Mixin, PickleEmbedded, PickleTest
 
 from mongoengine import *
-from mongoengine.base import _document_registry, NotRegistered
+from mongoengine.base import _document_registry, NotRegistered, InvalidDocumentError
 from mongoengine.connection import _get_db
 
 
@@ -2336,6 +2336,15 @@ class DocumentTest(unittest.TestCase):
         pickle_doc.reload()
         self.assertEquals(resurrected, pickle_doc)
 
+    def throw_invalid_document_error(self):
+
+        # test handles people trying to upsert
+        def throw_invalid_document_error():
+            class Blog(Document):
+                validate = DictField()
+
+        self.assertRaises(InvalidDocumentError, throw_invalid_document_error)
+
 
 if __name__ == '__main__':
     unittest.main()