i'm unable to get list of all the users who joined channel through presence in elixir, phoenix - sockets

Question

this is a quiz channel and after joining I want to get all the users who joined all the quizzes
quiz channel
def join("quiz:" <> id, _params, socket) do
presence = Nuton.Presence.list("quiz:" <> id)
if presence == %{} do
send(self(), {:after_join_quiz, id})
response = %{message: "you can now listen"}
{:ok, response, socket}
else
quiz = "quiz:#{id}"
%{^quiz => %{metas: metas}} = presence
if Enum.count(metas) > 1 do
{:error, %{reason: "Some other user already accepted the invitation"}}
else
send(self(), {:after_join_quiz, id})
response = %{message: "you can now listen"}
:ok = ChannelWatcher.monitor(:quiz, self(), {__MODULE__, :leave, [id]})
{:ok, response, socket}
end
end
end
def handle_info({:after_join_quiz, id}, socket) do
presence = Presence.list(socket)
if presence == %{} do
{:ok, _} =
Presence.track(socket, "quiz:" <> id, %{
user_name: socket.assigns.current_user.username,
user_id: socket.assigns.current_user.id,
quiz_id: id
})
{:noreply, socket}
else
{:ok, _} =
Presence.track(socket, "quiz:" <> id, %{
user_name: socket.assigns.current_user.username,
user_id: socket.assigns.current_user.id,
quiz_id: id
})
Core.Endpoint.broadcast(
"user:all",
"invitation:decline",
%{message: "Some other user already accepted the invitation"}
)
{:noreply, socket}
end
end
with specific quiz_id I can get all the user who joined the channel but with all I cant is there any issue in my code plz check if it is
Controller
quiz_users = Nuton.Presence.list("quiz:all")

Answer 1

You'd need to cycle through all of the channels, somehow, to get that information. I believe there was a PR to get this info, before, actually, so you can cycle through all.
What would be better: if you have the socket join 2 channels, like a "lobby" or "all" channel and then each individual channel. When you track, you can specify the string for the topic instead of only putting in the socket:
track(socket, "quiz:all", socket.assigns.user.id,%{})