Is there a way to get presences list inside a controller?

Question

I'm trying to get the presences list inside a phoenix controller, but I need the socket to use the function Presence.list(socket).

Anyone knows how to use Presence.list(socket) inside a controller? The reason why I am trying this is that I want to find a different user in my database than those connected to the channel (presence list).

score 2 · Accepted Answer · answered Jan 15 '19 at 17:25

2

The best way that I found was: Phoenix.Presence.list(MyApp.MyChannel, "my_topic")

There are the reference: Phoenix.Presence.list

answered Jan 15 '19 at 17:25

Andrés López Ferro

65
7

score 1 · Answer 2 · answered Jan 10 '19 at 15:50

Why don't you ask channel instead, just spawn synchronous task, join task to group to which you expect to receive result, then push message to channel and then return result back to controller as task completion result.

Let say this is controller action

    defmodule SomeController do
      #...
      def some_action(conn, params) do
        task = Task.async(fn ->
          MyApp.Endpoint.subscribe("topic:123:presence_list")
          MyApp.Endpoint.broadcast("topic:123", :presence_list, %{})
          receive do
            {:presence_list, list} ->
              {:ok, list}
          after
            5000 ->
              {:error, timeout}
          end
        end)
        {:ok, list} = Task.await(task)
        # do something with a list
      end
    end

Then in channel just handle broadcast and return Presence.list(socket)

This should be cleaner way instead of deigning into presence internals that may change in future.

Second option is to create your own tracker and plug it into app then ask your tracker to provide you a list of present users for specific channel. You can find some details how to implement tracker behaviour here

Is there a way to get presences list inside a controller?

2 Answers2