title: Rails: MassAssignmentSecurity::Error
body: <p>Following <a href="http://guides.rubyonrails.org/security.html#countermeasures" rel="nofollow">the ruby on rails guide</a> developer can't mass-assign protected fields but don't get exception trying to do it, right?
  But in my case mass-assignment different params through <code>new</code> method in <code>rails</code> application:</p>
  
  <pre><code>@edition = Edition.new params[:edition]
  </code></pre>
  
  <p>raise following exception:</p>
  
  <pre><code>ActiveModel::MassAssignmentSecurity::Error: Can't mass-assign protected attributes: price
  </code></pre>
  
  <p>Why? Did I understand something incorrectly? Is it a way not to get the mass-assignment exception? It's not convenient to delete protected attributes from hashes before assignments i think.</p>
  
  <p><strong>Update:</strong> Edition model:</p>
  
  <pre><code>class Edition &lt; ActiveRecord::Base
    attr_accessible :title, :description
    attr_protected :price
  end
  </code></pre>
  
  <p><code>params[:edition].inspect</code>:</p>
  
  <pre><code>{"title"=&gt;"t", "description"=&gt;"d", "price"=&gt;"123"}
  </code></pre>