Put_flash for log out method don't shows the message

Phoenix Forum Questions / Help
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1

Hello Guys,
first all I’m loving this book and it’s very helpfull.
I am reading now the version P1.0 of the ebook.
But I was in the part of ‘Log Out’ the session and I notice there they isn’t using a put_flash . And I would like to inform with a message.
So I try to put this:

  def delete(conn, _) do
    conn
    |> RumblWeb.Auth.logout()
    |> put_flash(:info, "Bye, Bye!")
    |> redirect(to: Routes.page_path(conn, :index))
  end

And when I test in the browser, this doesn’t shows the flash message.
Why this occur? It’s why we are dropping the session?
I’m asking just for clarify.

And another question is, why in the plug RumblWeb.Auth.logout don’t uses the clear_session(conn) like this:

def logout(conn) do
    conn
    |≥ clear_session()
    |≥ configure_session(drop: true)
  end

I’m asking because I saw using this in another example and why don’t was used here?
:v:

And in other part of the book:

If you want to keep the session around, you could also delete only the user ID information by calling delete_session(conn, :user_id) .

This part I don’t know why it was confusing and I want to understand better. In which cases this will serve for example? can Anyone explain better?
I’ll appreciate! :kissing_heart:

2 
template = https://media.pragprog.com/titles/{book_id}/code/{listing_title}
book_id = phoenix14
listing_title = authentication/listings/rumbl/lib/rumbl_web/controllers/session_controller.change2.ex

https://media.pragprog.com/titles/phoenix14/code/authentication/listings/rumbl/lib/rumbl_web/controllers/session_controller.change2.ex

If you use:

  # in rumbl/lib/rumbl_web/controllers/session_controller.ex
  def delete(conn,_) do
    IO.puts("RumblWeb.SessionController.delete: #{inspect(Routes.page_path(conn, :index))}")

    conn
    |> RumblWeb.Auth.logout()
    |> redirect(to: Routes.page_path(conn, :index))
  end

You should see this in the server console

RumblWeb.SessionController.delete: "/"

when you log out.

Phoenix.Controller.redirect/2

Sends redirect response to the given url.

So what is happening is that redirect/2 is instructing the browser to request “/” - the index page prepared by page_controller.ex.

The conn structure used for RumblWeb.PageController.index/2 is a fresh, new value. Whatever you put into the conn before the HTTP redirection has been lost …

https://media.pragprog.com/titles/phoenix14/code/authentication/listings/rumbl/lib/rumbl_web/controllers/auth.change2.ex

  def logout(conn) do
    configure_session(conn, drop: true)
  end

Plug.Conn.configure_session/2

  • :drop - drops the session, a session cookie will not be included in the response

… and in the absence of a session nothing carries over from one request to the next.

don’t uses the clear_session(conn)

Plug.Conn.clear_session/1

Note that, even if clear_session/1 is used, the session is still sent to the client. If the session should be effectively dropped , configure_session/2 should be used with the :drop option set to true .

i.e. given that the session is being dropped, clearing it is redundant.

In which cases this will serve for example?

Now change to this:

  # from rumbl/lib/rumbl_web/controllers/auth.ex
  def logout(conn) do
    delete_session(conn, :user_id)
    # configure_session(conn, drop: true)
  end

and this

  # in rumbl/lib/rumbl_web/controllers/session_controller.ex
  def delete(conn,_) do
    conn
    |> RumblWeb.Auth.logout()
    |> put_flash(:info, "Bye, Bye!")
    |> redirect(to: Routes.page_path(conn, :index))
  end

and you will see the flash info on the index page when you log out.

Plug.Conn.delete_session/2 simply deletes the value associated with the :user_id key from the session - but the rest of the session and all the other data in it remains - which is why now the flash info can carry over to the index page.

3 Likes
3

Minor nitpick, but you can write this as

IO.inspect(Routes.page_path(conn, :index), label: "RumblWeb.SessionController.delete")
4

IO.inspect/2 returns the value that it inspects - which can be useful in pipelines but here I have no interest in a return value and I want to directly annotate what is being output (though IO.inspect has the :label option).

5

Nice explanation @peerreynders, thank you very much for reply.
I’m loving the power of the Phoenix Framework.
I’ll expect to be very good using this framework.
And It’s a lot of things to learn… And I expect more books for learn with phoenix using the phoenix live view or react and vuejs.