title: Rails 3: Validating Model uniqueness of Time within a Time Range
body: <p>My model has start_time:time and end_time:time fields. What I want to be able to do is to check that the start_time to end_time range of my particular Reservation model does not overlap with any other reservations. </p>
  
  <p>So if there's a reservation from 4-6pm on Wednesday the 2nd, there can't be another reservation anytime from 4-6pm. How would I go about doing this? I'm not particularly sure as to how to validate Time ranges against other start_time,end_time tuples from the other Reservation entries. </p>