Question

My problem is to show modal with errors if submit is not successful.

I should try AJAX or it can be done without it?

I should override registration controller?

Answer 1

for example:

model User with some validations:

class User < ActiveRecord::Base
  validates :name,        :uniqueness => { :case_sensitive => false },
                          :presence => true
  validates :email,       :uniqueness => { :case_sensitive => false },
                          :presence => true,
  ...
end

I use a shared partial to display the errors that prevent the data in a form to be saved:

_error_messages.html.erb

<% if object.errors.any? %>
  <div id="error_explanation">
  <h3><%= pluralize(object.errors.count, "error") %>
    prohibited this <%= object.class.to_s.underscore.humanize.downcase %>
    from being saved:</h3>
  <p>There were problems with the following fields:</p>
  <ul>
  <% object.errors.full_messages.each do |msg| %>
    <li><%= msg %></li>
  <% end %>
  </ul>
  </div>
<% end %>

In the form to create or edit a new user:

<%= form_for(@user) do |f| %>
  <%= render 'shared/error_messages', :object => f.object %>
  <div class="field">
    <%= f.label :name %><br />
    <%= f.text_field :name %>
  </div>
...