Hello stackoverflow, I'm working on an Ruby on Rails application (2.3.x) and i want to make a form that lets the user login or register. I want to do this in the same form. I have a JS function that replaces the form elements like this: Login form: <% form_for @user do |f| %> <div id="form"> <%= f.label :email, "E-mail" %> <%= f.text_field :email %> <%= f.label :password, "Password" %> <%= f.password_field :password %> <%= link_to "I don't have an account, "#", :id => "changeForm"%> <%= f.submit "Login" %> </div> <% end %> The id "changeForm" triggers a JS function that changes the form elements. So if you press the url the html looks like this: <% form_for @user do |f| %> <div id="form"> <%= f.label :name, "Name" %> <%= f.text_field :name %> <%= f.label :email, "E-mail" %> <%= f.text_field :email %> <%= f.label :password, "Password" %> <%= f.password_field :password %> <%= f.label :password_confirmation, "Password confirmation" %> <%= f.password_field :password_confirmation %> <%= link_to "I do have an account, "#", :id => "changeForm"%> <%= f.submit "Register" %> </div> <% end %> I added the neccesary validations to my user model: class User < ActiveRecord::Base attr_reader :password validates_presence_of :name, :email, :password validates_format_of :email, :with => /\A([^@\s]+)@((?:[-a-z0-9]+\.)+[a-z]{2,})\Z/i validates_confirmation_of :password But what happens when you fill in the email / password you get the errors that the name is missing and that the password fields aren't confirmed. So i could do some nasty programming in my user model like this: #if password_conf or the name are present the user has tried to register... if params[:user][:password_confirmation].present? || params[:user][:name].present? #so we'll try to save the user if @user.save #if the user is saved authenticate the user current_session.user = User.authenticate(params[:user]) #if the user is logged in? if current_session.user.present? flash[:notice] = "succesvully logged redirect_to some_routes_path else #not logged in... flash[:notice] = "Not logged in" render :action => "new" end else #user not saved render :action => "new" end else #So if the params[:user][:password_confirmation] or [:user][:name] weren't present we geuss the user wants to login... current_session.user = User.authenticate(params[:user]) #are we logged_in? if current_session.user.present? flash[:notice] = "Succesvully logged in" redirect_to some_routes_path else #errors toevoegen @user.errors.add(:email, "The combination of email/password isn't valid") @user.errors.add(:password," ") render :action => "new" end end end Without validations this (imho dirty code and should not be in the controller) works. But i want to use the validates_presence_of methods and i don't want to slap the "conventions over configurations" in the face. So another thing i have tried is adding a hidden field to the form: #login form <%= f.hidden_field :login, :value => true %> # and ofcourse set it to false if we want to register. And then i wanted to use the method: before_validation before_validation_on_create do |user| if params[:user].login == true #throws an error i know... validates_presence_of :email, :password validates_format_of :email, :with => /\A([^@\s]+)@((?:[-a-z0-9]+\.)+[a-z]{2,})\Z/i else validates_presence_of :name, :email, :password validates_format_of :email, :with => /\A([^@\s]+)@((?:[-a-z0-9]+\.)+[a-z]{2,})\Z/i validates_confirmation_of :password end end But this doesn't work because i can't access the params. And login isn't a attribute for the user object. But i thought that in this way i could validate the email and password params if the user wants to login. And all the other attrs if the user want to register. So all i could think of doesn't work how i want it to work. So my main goal is this: 1 form for login/register with the use of the validation methods in the user model. So if we want to login but don't fill in any information = give validation errors. And if the user wants to login but the email/password combination doens't match give the "@user.errors.add(:email, "the combination wasn't found in the db...")". And the same goes for user register... Thanks in advance!