models: use unicode and not varchar

mandaye/models.py

@@ -10,14 +10,14 @@ from sqlalchemy import ForeignKey
 from sqlalchemy.ext.declarative import declarative_base
 from sqlalchemy.ext.mutable import Mutable
 from sqlalchemy.orm import column_property, relationship, backref
-from sqlalchemy.types import TypeDecorator, VARCHAR
+from sqlalchemy.types import TypeDecorator, Unicode
 
 Base = declarative_base()
 
 class JSONEncodedDict(TypeDecorator):
     "Represents an immutable structure as a json-encoded string."
 
-    impl = VARCHAR
+    impl = Unicode
 
     def process_bind_param(self, value, dialect):
         if value is not None: