title: Rails validate only in admin namespace
body: <p>In my rails app i have two user-logic:</p>
  
  <pre><code>user, and admin
  </code></pre>
  
  <p>for example my routing for line_item is such:</p>
  
  <pre><code>namespace :admin do
    resources :line_items, :only =&gt; [:edit, :update, :destroy]
  end
  resources :line_items, :only =&gt; [:new, :create, :update, :edit, :destroy]
  </code></pre>
  
  <p>but in admin part i must to do vailation for my line_item model:</p>
  
  <pre><code>  validates :notes, :presence =&gt; {:message =&gt;  I18n.t(:notes_not_chosen)}
    validates :quantity, :presence =&gt; {:message =&gt;  I18n.t(:quantity_not_chosen)}
    validates :price, :presence =&gt; {:message =&gt;  I18n.t(:price_not_chosen)}
    validates :description, :presence =&gt; {:message =&gt;  I18n.t(:description_not_chosen)}
  </code></pre>
  
  <p>But only in admin controller! How to do that i have validations only in admin  line_item controller, but didn't have in user part?</p>