Param in URL not passed to a form - Rails 4 - ruby-on-rails

Question

When accessing URL localhost:3000/buyers/sign_up?email=abc%40abc.com , the sign-up form is displayed but email field stays empty and is not auto-filled with abc#abc.com.
Could this be related to the implemented Single Table Inheritance (STI) ? -> Buyer inherits from User.
routes.rb
devise_for :users, :controller => {:sessions => 'sessions'}, :skip => :registrations do
delete '/logout', :to => 'sessions#destroy', :as => :destroy_user_session
get '/login', :to => 'sessions#new', :as => :new_user_session
post '/login', :to => 'sessions#create', :as => :new_user_session
end
devise_for :sellers, :skip => :sessions
devise_for :buyers, :skip => :sessions
resources :users
devise/registrations/new.html.erb
<%= form_for(resource, as: resource_name, url: registration_path(resource_name)) do |f| %>
<%= devise_error_messages! %>
<div><%= f.label :email %><br />
<%= f.email_field :email, autofocus: true %></div>
<div><%= f.submit "Sign up" %></div>
<% end %>
users_controller
class UsersController < ApplicationController
before_action :set_user, only: [:show, :edit, :update, :destroy]
def create
#user = User.new(user_params)
respond_to do |format|
if #user.save
format.html { redirect_to #user, notice: 'User was successfully created.' }
format.json { render action: 'show', status: :created, location: #user }
else
format.html { render action: 'new' }
format.json { render json: #user.errors, status: :unprocessable_entity }
end
end
end
private
# Use callbacks to share common setup or constraints between actions.
def set_user
#user = User.find(params[:id])
end
# Never trust parameters from the scary internet, only allow the white list through.
def user_params
params.require(:user).permit(:first_name, :last_name, :name, :type, :email)
end
end

Answer 1

Just found the answer.
Simply need to add value in the form + a condition to check presence of the e-mail param:
<%= f.email_field :email, value: params[:email] %>

Answer 2

Params
The problem isn't to do with STI - it's to do with how you're passing variables / parameters to your form.
You must remember that when you use form_for, Rails will automatically populate the provided HTML elements with data from the ActiveRecord object - in that if your object has the attribute email, the form will have that data populated
If you want to populate the form with new data (from a URL), you'll either have to be able to populate the #user.email attribute (as suggested by JTG), or take the params from the URL & pass them through to your form
--
The ways I would look at doing this would include:
Controller-based (the best)
Front-end "params" based
The controller method can be accessed as follows:
#app/controllers/users_controller.rb
Class UsersController < ApplicationController
def new
#user = User.new(email: params[:email])
end
end
This should work, as the param should be made available to the controller during the request.
-
The alternative, as you've discovered, is to populate the value of the element on your page:
<%= f.text_field :email, value: params[:email] %>
This will leave the :email field blank if no email parameter was / is defined.

Answer 3

Making a request to new#User (which is what you are requesting with /buyers/sign_up) won't autofill any of the sign_up form by default
However, you can put
def new
#user = User.new
#user.email = params[:email] if params.has_key? "email"
end
for the url
/buyers/sign_up?email=abc%40abc.com
And it should auto complete the email textfield of your form.
if your url was structured like so...
/buyers/sign_up?user[email]=abc%40abc.com
Then you should be able to use the much more elegant
def new
#user = User.new(params[:user])
end
in your new call. That way you can send in more than one parameter