title: How to set composite key in Rails application
body: <p>I am using 'foriegner' gem in my application to set primary key, now i am in a situation to 
  set composite primary key in a table.</p>
  
  <p>I searched the web for this, but could not able to find a clear solution for this.</p>
  
  <p>Please suggest me if its possible to set composite keys in rails application using foreigner gem or by any other means.</p>
  
  <p><strong>Note : I am using Postgres</strong></p>
  
  <p>thanks.</p>