Preserving form submission through log in / sign up in Rails

Say I have a site like this (generic Q&A site) 开发者_运维百科in Rails and I wanted this "ask" page w/ a text box to be the first page a user sees, even if he's not logged in. He enters a question, and on the 'new' method I check that he's not logged in, and bounced him to /session/new, where he can either log in or create a new account. Question is, how do I (and what is the best way to) preserve that question that he initially asked all through this process?

I'm understanding the flow of action described in the question to be

1. user is presented with a form
2. user is redirected to log in page on submit
3. user is redirected back to form on successful log in
4. repopulate form on load (Question asks how to do this step)
5. user finally submits their form.

With steps 2-4 omitted if the user is logged in.

I'm sorry, but I see your question more as a symptom of an underlying UI issue than a rails question.

If only logged in users can post questions, then why display the text box? If a user is going to have log in any way, why not get that out of the way first. An even better solution is to integrate the log in and form.

Something like this in the view:

<% form_for :question do |form| %>
  <% unless logged_in? %>
    <% fields_for :session do |session_form|%>
      <%= session_form.label :login %>
      <%= session_form.text_field :login %>
      <%= session_form.label :password %>
      <%= session_form.password_field :password %>
    <%end%>
  <%end%>
  <%= form.text_area :question %>
<%end%>

And in the controller

def new
  ...
  unless params[:session].nil?
    self.current_user = User.authenticate(params[:session][:login], params[:session][:password])
  end
  if logged_in? 
    flash[:notice] = "Logged in successfully"
  else 
    flash[:error] = "Incorrect username and or password."
  end
  if logged_in? && @question.save
    .... process successful entry
  else
    ... process unsuccessful entry
  end
end

Edit: Mohamad's raises the question of reusing this pattern across multiple controllers and forms. So the answer was updated to address reuse of this pattern.

To simplify this for reuse, you could put this block in a helper function that is referenced in the before_filter for actions that require it.

def login
  unless params[:session].nil?
    self.current_user = User.authenticate(params[:session][:login], params[:session][:password])
    if logged_in? 
      flash[:notice] = "Logged in successfully"
    else
      flash[:error] = "Incorrect username and or password."
    end
  end
end

as in:

before_filter :login => :only [:new , :edit, :update, :delete]

On the view side, it shouldn't be too hard to construct a new variant of form_for that embeds the session parameters. Maybe form_for_with_session?

As for handling an unsuccessful response, I would suggest helper function that takes a block of code. Sorry I don't have time to write out or test one for you.

You keep it in the session. So after logging in, when the user goes back to asking his question, you see there's already something in session.
And you can directly display it.

def create
  if current_user   # Implement this method in your auth framework
    @question = Question.new(params[:question] || session.delete[:question])
    # (the usual stuff you'd do to save)
  else
    session[:question] = params[:question]
    redirect_to :controller => :sessions, :action => "new"
  end
end

Then, after your user creation and authentication stuff is all done in your login action, just make sure you POST back to this create action if session[:question] is defined.