title: validates_uniqueness_of when updating car.number
body: <p>When updating car info, the validation process fails because I have validates_uniqueness_of :number</p>
  
  <pre><code>class Car &lt; ActiveRecord::Base
  validates :number,numericality: true, length: {is: 7 }
  validates :number, :name, presence:true
  validates_uniqueness_of :number, :message =&gt; "מספר רכב זה קיים במערבת"
  belongs_to :owner
  has_many :visits
  end
  </code></pre>
  
  <p>I need validation to pass, if the original value was not changed, validation on_create would not help since I still need validation when updating.</p>
  
  <p>Any help would be really appreciated.</p>