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Elixir passing value while redirection

login function should take the variable provided by the user in the form, and then is checking if the given user exists in the database. If yes, he will be redirected to main site, if not, he will be redirected to the same form to submit again his name. I have two problems.

Both put_flash functions don't work.
I do not know how to pass additional values from login (while redirect there is userp: userp value, which is not provided in the :main, and not in the render in the :main). How could I add these additional arguments? Right now it only keeps user name, but later on I want it to handle the whole user specification from the database (it is working right now). Below is code

login function:

  def login(conn, %{"user" => userp}) do
    changeSet = RewardappWeb.User.changeset(%RewardappWeb.User{}, userp)
    #IO.inspect(userp)
    users = Rewardapp.Repo.all(RewardappWeb.User)
    #IO.inspect(changeSet)

    #VALIDATION, IF GIVEN USER BELONGS TO DATABASE

    value = userp["user"]

    #map of lists
    listOfUsers = Rewardapp.Repo.all(RewardappWeb.User)

    IO.inspect(Enum.find(listOfUsers, fn x -> x.name == value end))

    userSpec = Enum.find(listOfUsers, fn x -> x.name == value end)

    IO.inspect(userSpec)

    case userSpec do
      nil ->
        put_flash(conn, :error, "Could not find the user")
        #render(conn, "index.html", users: users, changeSet: changeSet)
        redirect(conn, to: Routes.grant_path(conn, :index), users: users, changeSet: changeSet)
      _ ->
        put_flash(conn, :info, "Logged in")
        #render(conn, "start.html", changeSet: changeSet, users: users, userp: userp)
        redirect(conn, to: Routes.grant_path(conn, :main), users: users, changeSet: changeSet, userp: userp)
    end

  end

main function:

  def main(conn, params) do
    changeSet = RewardappWeb.User.changeset(%RewardappWeb.User{}, %{})
    users = Rewardapp.Repo.all(RewardappWeb.User)
    render(conn, "start.html", changeSet: changeSet, users: users)
  end

index function :

  def index(conn, params) do
    changeSet = RewardappWeb.User.changeset(%RewardappWeb.User{}, %{})
    render(conn, "index.html", changeSet: changeSet)
  end

the router.ex looks like this:

get "/main", GrantController, :main
get "/", GrantController, :index
post "/users", GrantController, :login

Thanks you in advance for any helping!!!

over 4 years ago · Santiago Trujillo

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Answer 1 · 2022-04-13T21:35:27.258Z

Elixir is a functional language. You can't mutate "classes" in place and then use them after mutation, or anything like that.

case userSpec do
  nil ->
    put_flash(conn, :error, "Could not find the user")
    redirect(conn, to: Routes.grant_path(conn, :index), users: users, changeSet: changeSet)
  # ...
end

Your put_flash(conn, ...) call will create a modified conn and throw it into the ether.

Then the redirect(conn, ...) call will modify the original conn (the one without the flash, not the one with the flash) and that's what your login function actually ends up returning.

So that's why the redirect works, but there is no plash - it wasn't added to the conn you're returning.

So what you want to do is something like

case userSpec do
  nil ->
    conn 
    |> put_flash(:error, "Could not find the user")
    |> redirect(to: Routes.grant_path(conn, :index), users: users, changeSet: changeSet)
  # ...
end

I.E. you add the flash to the conn, then redirect the result, and that's what your function should return.

I hope that helps.

As for adding additional arguments to the redirect, it depends on what you want to add. If it's query params, then you could do

path = Routes.grant_path(conn, :index, %{"foo" => "bar"})
redirect(conn, to: path)

The other way to add data would be to put it in session.

I'm guessing what you actually want is add data that is then used in the html you're rendering. Redirection doesn't work that way. It's basically telling the browser, go to this other location and go through the request process from the beginning.

In some cases, you might be able to render a different view template, rather than redirecting and achieve what you want.

render(conn, "index.json", user: user, changeset: changeset)

But whether that's possible here really depends on your specific case.

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Elixir passing value while redirection

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Andres GPT