How to make errored inputs prepopulate with previously inputted data - ruby-on-rails

Question

I'm making a custom AJAX form.
If a user fills out half of the form, it will fail wanting the other half fulfilled.
For some odd reason, the form is not pre-populating with at least what they had already inputted.
Because it's not doing this, how can I manually tell it to do so? When the form returns, the Object it verified is still accessible, so I can withdraw information from it.
a sample of the form
- form_for CardSignup.new do |f|
- unless #card_signup.nil?
- if !#card_signup.errors.empty?
.prefix_1.grid_4
- #card_signup.errors.full_messages.each do |error|
.warning
= error
%br/
.grid_2.prefix_1{:style => "width: 166px;"}
= f.text_field :first_name, :style => "width: 166px;", :value => "first name", :rel => "first name"
%div{:class => 'error_message'}
my Create method
def create
if params[:user] && current_user.admin
#card_signup = User.find(params[:user]).build_card_signup(params[:card_signup])
else
#card_signup = current_user.build_card_signup(params[:card_signup])
end
if #card_signup.valid?
respond_to do |wants|
#wants.html { redirect_to disclaimer_card_signup_path, :locals => { :card_signup => #card_signup } }
wants.json { render :json => { :html => (render_to_string :partial => 'disclaimer') } }
end
else
respond_to do |wants|
#wants.html { redirect_to new_card_signup_path }
wants.json { render :json => {:errors => #card_signup.errors, :html => (render_to_string :partial => '/card_signups/new_form') } }
end
end
end

Answer 1

You're doing this:
form_for CardSignup.new
which will instantiate a new CardSignup object every time you render the form. Move this into the new action and in the create action do this:
#card_signup = CardSignup.new(params[:card_signup])
This will pass the half-filled object back to the form and you'll get the already populated fields.