How does session work in LiveView

vfsoraki

In mount/3 callback of a LiveView module, you get session as the second parameter. It works fine, until you use live_redirect/push_redirect to mount another LiveView.

In this case, what is the session passed to second one? The same as original?

Is there a way to change it, without some hacky thing?

I currently did it by using JS to append some signed query string to my url and reload the page, and a plug that reads that signed string and sets appropriate session values, but this feels kind of hacky.

My current use case is user settings page. User changes some settings, then hits save, then goes to another page. User settings is saved in database, but session data is still old, so when new LiveViews are mounted they still see the old setting.

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/phoenix #session #liveview

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2021-08-04 23:46:49 UTC

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wanton7

I might be wrong here because of my limited usage of LiveView. But if session is same as Phoenix session my understanding is that default implementation uses a cookie to save session values. Because LiveView uses Websocket it can’t create a cookie for browser. You likely have to look for alternative to session cookie implementation.

Post #1

vfsoraki

That’s something I failed to mention, though I don’t think will matter.

I’m not using cookies for session storage. I’m using a custom implementation that uses database for session storage. It’s an implementation for Plug.Session, so I don’t think it should matter what is my session storage.

Post #2

wanton7

How do match session to database values? I mean you probably still have a cookie that has a session id right? Maybe that cookie isn’t created?

Post #3

vfsoraki

I do have sessions working fine in normal HTTP requests. It works fine, and my session store also works fine. LiveView also gets the first session correctly.

Yes, only session id is saved in a cookie, and session data is stored in database.

I just implemented a store using Plug.Session.Store — Plug v1.20.2. Thats all, nothing tricky or fancy.

Maybe I should’ve reworded my question to something like “How to modify session when using LiveView, without refreshing the page?”

Post #4

derek-zhou

Presumably the session id will not change because the user changing their settings. You can just load whatever stuff from the database at the mount time of the liveview, right?

Post #5

vfsoraki

No, session id will not change when it’s modified.

Consider session has user key which has the data for current user. I can read this using def mount(_, %{"user" => user}, socket) in LiveView, but when I change user in anyway, there is no way to update session, presumably because there is no conn.

EDIT: I mean without a full refresh of course, like what live_redirect/push_redirect does.

Although one might say that session id is stored in a cookie, and that can be read by LiveView and it can also be modified then, but I think there is no way to do it right now.

I can reload my user in every LiveView like:

def mount(_, %{"user" => %{id: user_id}}, socket) do
  {:ok, assign(socket, user: Users.get!(user_id))}
end

But I think there may be a better way.

Post #6

derek-zhou

What do you mean by a better way? In plain HTTP you read it every time in your plug. In live_redirect your plug did not run so you would need to read it yourself in mount.

Post #7