Rails in practice - Compare records

July 06 2007 rails tips

Rails in practice - Compare records

We have Travel object which defines travel_on attribute. Now, when I want to compare Travel objects, I can use:

raise "Cannot come before you leave" unless departure.travel_on > arrival.tavel_on

Or sort travel array with:

journeys.sort {|a,b| a.travel_on<=>b.travel_on}

This would work, but it is not very readable and DRY. If we include Comparable mixin in Travel , and define <=> operator we would get conventional comparison operators (<, <=, ==, >=, and >) including the method between? for free. Our code would now look:

class Travel < ActiveRecord::Base
  include Comparable

  def <=>(other)
    self.travel_on<=>other.travel_on
  end  
end
...
raise "Cannot come before you leave" unless departure > arrival
...
journeys.sort
...
some_other_travel.between?(arrival, departure)