Client Side Validations

//account.rb

   validates :namauser, presence: true, uniqueness: true

//user.rb
 belongs_to :account
 validates :email, presence: true, uniqueness: true

//new.html.erb

<%= form_for(@user, :url => registration_path(resource_name), :validate => true) do |f| %>

   <%= f.fields_for :account, :validate => true do |inner_form|%>
      <div  class="field">
          <%= inner_form.label :namauser, "Nama User" %><br />
          <%= inner_form.text_field :namauser %>
      </div>
   <% end %>

   <div class="field">
       <%= f.label :email, "Email" %>
       <%= f.email_field :email %>
   </div>
   <div>
       <%= f.submit "Sign up" %>
   </div>

<% end %>