throw ResourceNotFoundException and not AccessDeniedException
removed duplicating UserService#findOne method
added property unseen to subscription entity. indicates new unseen entries for given subscription. added pesimistici locking to feed and subscription in order to maintain correct values in aggregation columns "fetched", "sum" and "unseen"
added pessimistic_read lock to (Feed|Subscription)Repository#findOne
expose unseen aggregate
refresh subscription unseen aggregates on context refresh event