title: Friendly_id creating duplicate slugs for multiple objects in Rails
body: <p>My Rails build contains no pathnames. The application consists of two main objects: <code>collections</code> and <code>items</code>. So if I have a link: <a href="https://foo.com/foo" rel="nofollow">https://foo.com/foo</a>, this could potentially identify either a collection or an item. The difference is made clear within the context and UI flow throughout the application. </p>
  
  <p>My question: is there a way to have the Friendly ID gem generate unique slugs by seeing if a slug has already been taken by another object? I understand you can generate candidates so that friendly ID will not duplicate a slug for a given object, but I need friendly ID to check both existing collection slugs and item slugs before generating a new slug. </p>
  
  <p>I hope that didn't sound too confusing. To re-word more concisely: is there a method available for friendly ID to check for slugs in multiple objects before generating a new slug?</p>