Fixes saving document schemas that have changed

Ensures that form defaults which are documents are
automatically marked as changed, so schemas can evolve
without migration issues.

[#360]

AUTHORS

@@ -74,4 +74,5 @@ that much better:
  * Marc Tamlyn
  * Karim Allah
  * Adam Parrish
+ * jpfarias
 

docs/changelog.rst

@@ -5,6 +5,7 @@ Changelog
 Changes in dev
 ==============
 
+- Fixed document mutation saving issue
 - Fixed positional operator when replacing embedded documents
 - Added Non-Django Style choices back (you can have either)
 - Fixed __repr__ of a sliced queryset

mongoengine/base.py

@@ -883,14 +883,21 @@ class BaseDocument(object):
                     """.strip() % class_name)
             cls = subclasses[class_name]
 
+        changed_fields = []
         for field_name, field in cls._fields.items():
             if field.db_field in data:
                 value = data[field.db_field]
                 data[field_name] = (value if value is None
                                     else field.to_python(value))
+            elif field.default:
+                default = field.default
+                if callable(default):
+                    default = default()
+                if isinstance(default, BaseDocument):
+                    changed_fields.append(field_name)
 
         obj = cls(**data)
-        obj._changed_fields = []
+        obj._changed_fields = changed_fields
         return obj
 
     def _mark_as_changed(self, key):

tests/document.py

@@ -2360,6 +2360,36 @@ class DocumentTest(unittest.TestCase):
 
         self.assertRaises(InvalidDocumentError, throw_invalid_document_error)
 
+    def test_mutating_documents(self):
+
+        class B(EmbeddedDocument):
+            field1 = StringField(default='field1')
+
+        class A(Document):
+            b = EmbeddedDocumentField(B, default=lambda: B())
+
+        A.drop_collection()
+        a = A()
+        a.save()
+        a.reload()
+        self.assertEquals(a.b.field1, 'field1')
+
+        class C(EmbeddedDocument):
+            c_field = StringField(default='cfield')
+
+        class B(EmbeddedDocument):
+            field1 = StringField(default='field1')
+            field2 = EmbeddedDocumentField(C, default=lambda: C())
+
+        class A(Document):
+            b = EmbeddedDocumentField(B, default=lambda: B())
+
+        a = A.objects()[0]
+        a.b.field2.c_field = 'new value'
+        a.save()
+
+        a.reload()
+        self.assertEquals(a.b.field2.c_field, 'new value')
 
 if __name__ == '__main__':
     unittest.main()