q_sub_sender.setAncestor(sub_key);
q_sub_sender.setKeysOnly();
q_sub_sender.addFilter(SUBSCRIPTION_EMAIL_PROPERTY, FilterOperator.EQUAL, sender);
q_sub_sender.addFilter(SUBSCRIPTION_STATUS_PROPERTY, FilterOperator.EQUAL, "Active");
PreparedQuery pq_sender = datastore.prepare(q_sub_sender);
Entity sender_entity = pq_sender.asSingleEntity();
if(sender_entity == null)
return false;
Key sender_key = sender_entity.getKey();
Transaction txn = datastore.beginTransaction();
Entity sender_feed = new Entity(FEED_KIND, sender_key);