validate db_field

mongoengine/base/fields.py

@@ -81,6 +81,17 @@ class BaseField(object):
         self.sparse = sparse
         self._owner_document = None
 
+        # Validate the db_field
+        if self.db_field and (
+            '.' in self.db_field or
+            '\0' in self.db_field or
+            self.db_field.startswith('$')
+        ):
+            raise ValueError(
+                'field names cannot contain dots (".") or null characters '
+                '("\\0"), and they must not start with a dollar sign ("$").'
+            )
+
         # Detect and report conflicts between metadata and base properties.
         conflicts = set(dir(self)) & set(kwargs)
         if conflicts:

tests/fields/fields.py

@@ -306,6 +306,24 @@ class FieldTest(unittest.TestCase):
         person.id = '497ce96f395f2f052a494fd4'
         person.validate()
 
+    def test_db_field_validation(self):
+        """Ensure that db_field doesn't accept invalid values."""
+
+        # dot in the name
+        with self.assertRaises(ValueError):
+            class User(Document):
+                name = StringField(db_field='user.name')
+
+        # name starting with $
+        with self.assertRaises(ValueError):
+            class User(Document):
+                name = StringField(db_field='$name')
+
+        # name containing a null character
+        with self.assertRaises(ValueError):
+            class User(Document):
+                name = StringField(db_field='name\0')
+
     def test_string_validation(self):
         """Ensure that invalid values cannot be assigned to string fields.
         """
@@ -3973,30 +3991,25 @@ class FieldTest(unittest.TestCase):
         """Tests if a `FieldDoesNotExist` exception is raised when trying to
         instanciate a document with a field that's not defined.
         """
-
         class Doc(Document):
-            foo = StringField(db_field='f')
+            foo = StringField()
 
-        def test():
+        with self.assertRaises(FieldDoesNotExist):
             Doc(bar='test')
 
-        self.assertRaises(FieldDoesNotExist, test)
 
     def test_undefined_field_exception_with_strict(self):
         """Tests if a `FieldDoesNotExist` exception is raised when trying to
         instanciate a document with a field that's not defined,
         even when strict is set to False.
         """
-
         class Doc(Document):
-            foo = StringField(db_field='f')
+            foo = StringField()
             meta = {'strict': False}
 
-        def test():
+        with self.assertRaises(FieldDoesNotExist):
             Doc(bar='test')
 
-        self.assertRaises(FieldDoesNotExist, test)
-
     def test_long_field_is_considered_as_int64(self):
         """
         Tests that long fields are stored as long in mongo, even if long value