How to render a view from a view using a condition?

Question

I'm testing out RoR and am currently trying to figure out the functionality which allows users with a valid session to skip logging in.

The login button usually prompts you to a login page, whereas I want to make it so that people with a session skip it and immediately get redirected to the show view using a conditional statement. (Checks via current_user) (If you need any other code just comment)

Here's the login view

<%= form_for :session, url: '/login' do |s| %>
<%= s.text_field :username, :placeholder => 'Username' %>
<%= s.password_field :password, :placeholder => 'Password' %>
<%= s.submit "Login" %>

<% if current_user %>
    <!-- What do i write here? -->
    <!-- Maybe I should put this in a controller? -->
    <% end %>

<% if flash[:notice] && current_user %>
    <div class="notice"><%= flash[:notice] %></div>
<% end %>

Here's the application controller containing the current_user function. (just in case)

class ApplicationController < ActionController::Base
protect_from_forgery with: :exception

helper_method :current_user

 def current_user
   @current_user ||= User.find_by(id: session[:id]) if session[:id]
 end
end

Answer 1

Not sure what your SessionsController looks like, but you could add something like this:

class SessionsController < ActionController::Base
  before_action :check_current_user

  def check_current_user
    redirect_to :root, success: "You are already logged in." if current_user
  end
end

Then you can remove the if current_user statement in your login view. And for your login links you could write:

<%= link_to 'Login', new_session_path unless current_user %>

This way the login button only shows if current_user is nil.

Also, take a look at Rails Tutorial Chapter 8: Basic Login for more information

Answer 2

Within your view you can render partials with the render method if you just want to show the login button to users that are not logged in:

<% unless current_user %>
  <%= render 'login_form' %>
<% end %>

Then you need to have a file named '_login_form' in your view directory:

<%= form_for :session, url: '/login' do |s| %>
<%= s.text_field :username, :placeholder => 'Username' %>
<%= s.password_field :password, :placeholder => 'Password' %>
<%= s.submit "Login" %>