How to pass data from the assigns in the first mount call to the second mount in LiveView

Phoenix Forum Questions / Help
1

Hello,

I am building a website that has several agencies, each of them, related to one domain.

I need to get the agency data in the assigns, similar to what we do with :current_user.

The user information is stored in the session, but I can’t do that. It won’t make sense store the agency information in the session.

What I have done:

  1. I have added plug :fetch_current_agency to the browser pipeline. For testing purposes the function does nothing yet, but return an arbitrary string:
  def fetch_current_agency(conn, _opts) do
    # Here I should return and %Agency{} but for simplicity and testing purposes
    # I return the host only
    assign(conn, :agency, conn.host)
  end
  1. On the on_mount callback, I call :ensure_agency. This is the function:
def on_mount(:ensure_agency, _params, session, socket) do
    # Note the agency fallback is only for testing purposes and to make the code simpler
    socket = Phoenix.Component.assign_new(socket, :agency, fn -> "Agency fallback" end)

    IO.puts("Socket agecny: #{socket.assigns.agency}")

    {:cont, socket}
end

On the on_mountcallback, I get the agency right in the first mount call, which is the host. But on the second time, I get the fallback value Agency fallback

My question is, how can I persist the agency data in the assigns?

In this simplified code, I’d like to have the host’s value on the assigns every time so I can access it later in the live views.

Thanks!

2
3 Likes
3

Thanks @LostKobrakai ! Your article is very good and helped me to find a way to implement what I need.

After reading it, I investigated how the session data is passed to the WebSocket, and I learned about Phoenix.LiveView.Socket and the connect_info parameters.

I found in the docs of get_connect_info/2 that it accepts the parameters: :peer_data, :trace_context_headers, :x_headers, :uri, and :user_agent.

And :uri is exactly what I need!

More valuable docs in the Phoenix Endpoint

I inspected the WebSocket and saw the session data but not the URI data. Is it encoded inside the session?

Thanks!

4

You explicitly need to tell the socket which information you need in the connect info. E.g. directly from the macro documentation for socket/3:

socket "/socket", AppWeb.UserSocket,
      websocket: [
        connect_info: [:peer_data, :trace_context_headers, :x_headers, :uri, session: [store: :cookie]]
      ]