title: Validating Uniqueness Across Two Tables
body: <p>I have a <code>Company</code> and <code>Archive</code> model that have the same table structure. Both models have a <code>validates :name, :uniqueness =&gt; true</code> validation. </p>
  
  <p>In the company.rb file  I'm having trouble setting up a custom validation where when I add a record to the <code>Company</code> database it also checks the <code>Archive</code> model (so that if a record in the Archive model with that name already exists then it won't be added to the <code>Company</code> table).</p>
  
  <p>I'm assuming this is possible to do, but I'm having trouble implementing, can anyone help?  </p>