Check if undefined fields are supplied on document

If an undefined field is supplied to a document instance, a
`FieldDoesNotExist` Exception will be raised.

mongoengine/base/document.py

@@ -12,7 +12,7 @@ from bson.son import SON
 from mongoengine import signals
 from mongoengine.common import _import_class
 from mongoengine.errors import (ValidationError, InvalidDocumentError,
-                                LookUpError)
+                                LookUpError, FieldDoesNotExist)
 from mongoengine.python_support import PY3, txt_type
 
 from mongoengine.base.common import get_document, ALLOW_INHERITANCE
@@ -61,6 +61,15 @@ class BaseDocument(object):
 
         signals.pre_init.send(self.__class__, document=self, values=values)
 
+        # Check if there are undefined fields supplied, if so raise an
+        # Exception.
+        for var in values.keys():
+            if var not in self._fields.keys():
+                msg = (
+                    "The field '{}' does not exist on the document '{}'"
+                ).format(var, self._class_name)
+                raise FieldDoesNotExist(msg)
+
         if self.STRICT and not self._dynamic:
             self._data = StrictDict.create(allowed_keys=self._fields_ordered)()
         else:

mongoengine/errors.py

@@ -40,6 +40,10 @@ class NotUniqueError(OperationError):
     pass
 
 
+class FieldDoesNotExist(Exception):
+    pass
+
+
 class ValidationError(AssertionError):
     """Validation exception.