Moved old legacy code to toolbox, also allowing the LegacyEmbeddedMod…

…elField to be used to avoid converting / deconverting embedded instance fields' values -- as it works now.

django_mongodb_engine/fields.py

@@ -8,25 +8,26 @@
 from djangotoolbox.fields import EmbeddedModelField as _EmbeddedModelField
 from django_mongodb_engine.utils import make_struct
 
+
 __all__ = ['LegacyEmbeddedModelField', 'GridFSField', 'GridFSString']
 
+
 class LegacyEmbeddedModelField(_EmbeddedModelField):
     """
-    Wrapper around djangotoolbox' :class:`EmbeddedModelField` that keeps
-    backwards compatibility with data generated by django-mongodb-engine < 0.3.
+    Wrapper around djangotoolbox' :class:`EmbeddedModelField`
+    that keeps backwards compatibility with data generated by
+    older versions of the back-end.
+
+    In version 0.2 the layout of serialized model instances changed:
+    the _app key is not stored anymore, while a _model name must be
+    accompanied by a _module key, also _id's were added automatically.
+
+    In version 0.6? we started to pass embedded instance fields' values
+    through back-end database type conversion / deconversion (e.g. key
+    value -> ObjectId).
     """
-    def to_python(self, values):
-        if isinstance(values, dict):
-            # In version 0.2, the layout of the serialized model instance changed.
-            # Cleanup up old instances from keys that aren't used any more.
-            values.pop('_app', None)
-            if '_module' not in values:
-                values.pop('_model', None)
-            # Up to version 0.2, '_id's were added automatically.
-            # Keep backwards compatibility to old data records.
-            if '_id' in values:
-                values['id'] = values.pop('_id')
-        return super(LegacyEmbeddedModelField, self).to_python(values)
+    pass
+
 
 class GridFSField(models.Field):
     """