title: Rails 3 validates rule based on action
body: <p>This seems like a simple question but I can't seem to find an answer short of writing custom validators. I have this validator</p>
  
  <pre><code>validates :password, :presence =&gt; true, :confirmation =&gt; true, :length =&gt; { :minimum =&gt; 5}
  </code></pre>
  
  <p>there are more rules applied such as some regex for complexity, but this gives the gist.</p>
  
  <p>The issue is that I only want presence applied on create, everything else needs to be on create and update. Because the user may not be changing a password when updating their information.</p>
  
  <p>I tried splitting the rules</p>
  
  <pre><code>validates :password, :presence =&gt; true, :on =&gt; :create
  validates :password, # The rest of the rules
  </code></pre>
  
  <p>This resulted in all rules being ignored for update. Is there a simple way to apply only one rule to create and the rest to everything?</p>