title: has_many relation with conditions
body: <p>I have a Model (user) that has_many :bookings</p>
  
  <p>bookings have a complete field</p>
  
  <p>Id like to be able to view all the bookings for a user where the booking complete is true
  I'd also like to be able to sometimes show all the bookings for a user regardless of complete</p>
  
  <p>Whats the best way to set this up in my models? </p>