title: RailsAdmin - Customizing your own filters
body: <p>I'm using <a href="https://github.com/sferik/rails_admin">https://github.com/sferik/rails_admin</a> to handle my admin interface.</p>
  
  <p>It's possible to filter your model based on the current columns that exists in this model (id, created_at etc.)</p>
  
  <p>I want to be able to add custom filters for associations.</p>
  
  <p>For example:</p>
  
  <p>When I'm exploring the "Towns" model I want to be able to show only towns that have one or more projects.</p>
  
  <p>I could do this by adding a new column to towns, called has_projects as a boolean that will be set to true when there are 1 or more projects associated, but I feel there must be a cleaner way to make your own custom filters ?</p>