anchor.diff:      {reply, do_update_device(State, Rec), State};
   handle_call({delete_device, Rec}, _From, State) ->
       {reply, do_delete_device(State, Rec), State};
  -handle_call({get_device, Query}, _From, State) ->
  -    {reply, do_get_device(State, Query), State};
   handle_call({get_devices}, _From, State) ->
       {reply, do_get_devices(State), State};
   
  
positive.code:          create_permission/1,
           delete_permission/1,
           get_permissions/0,
           get_permission/2,
           get_permissions_by_user_id/1,
           get_permissions_by_device_id/1,
  
           create_user/1,
           update_user/1,
           delete_user/1,
           get_user_by_id/1,
           get_user_by_email/1,
           get_users/0,
  
           create_device/1,
           update_device/1,
           delete_device/1,
           get_device_by_id/1,
           get_device_by_uid/1,
           get_devices/0,
  
           create_position/1,
  
negative.code: update_user(Rec) ->
      gen_server:call(?SERVER, {update_user, Rec}).
  
  -spec(get_users() -> {ok, [#user{}]} | {error, string() | [string()]}).
  get_users() ->
      gen_server:call(?SERVER, {get_users}).
  