implemented from_db_value in PowerZOnes model

rowers/models.py

@@ -53,7 +53,7 @@ if settings.DEBUG or user=='':
 
 # model for Power Zone names
 class PowerZonesField(models.TextField):
-    __metaclass__ = models.SubfieldBase
+#    __metaclass__ = models.SubfieldBase
 
     def __init__(self, *args, **kwargs):
         self.token = kwargs.pop('token',',')
@@ -65,6 +65,13 @@ class PowerZonesField(models.TextField):
             return value
         return value.split(self.token)
 
+    def from_db_value(self,value, expression, connection, context):
+        if value is None:
+            return value
+        if isinstance(value, list):
+            return value
+        return value.split(self.token)
+    
     def get_db_prep_value(self, value, connection, prepared=False):
         if not value: return
         assert(isinstance(value, list) or isinstance(value, tuple))