Random banners for specific position with random order

Banner.rb

# Show banners for fixed position with some visibility and date range limits.
# Also return banners in random order.

# Use like so:
# Banner.for_position('a').each do { |b| b... }

# Tested with postgresql, sqllite and rails 3.1...

def self.for_position(position = 'a', for_date=DateTime.now.to_date)
  where("position = ?", position)
  .where("? between from_date AND to_date", for_date)
  .where("hidden = 0")
  .order("RANDOM()")
  .limit(
    [(2 if position=='a'),
      (4 if position=='b'),
      (1 if position=='c')].compact.first
  )
end