anchor.diff:      Reason ->
         {reply, Reason, State}
     end.
  +
  +do_delete_device(State = #state{cache = Cache}, DeviceModel) ->
  +  case em_storage:delete_device(DeviceModel) of
  +    {ok, Device} ->
  +      case ets:delete(Cache, Device#device.id) of
  +        true ->
  +          {reply, {ok, Device}, State};
  +        false -> {reply, {error, <<"Error sync in devices cache">>}, State}
  +      end;
  +    Reason ->
  +      {reply, Reason, State}
  +  end.
positive.code: -spec(update(Device :: #device{}) -> {ok, #device{}} | {error, string()}).
  update(Device) ->
    gen_server:call(?SERVER, {update, Device}).
  
  %%--------------------------------------------------------------------
  %% @doc
  
negative.code: -export([
    get/0,
    create/1,
    update/1,
    delete/1
  ]).
  
  %% gen_server callbacks
  