dates as string

model.js

var dateComputed = function(prop) {
  var mProp = prop + 'Month',
      yProp = prop + 'Year';
      
  return Ember.computed(mProp, yProp, function(key, value) {
    if (arguments.length == 2) {
      // setter... maybe moment.js
    } else {
      // getter... maybe moment.js
    }
  });
}

App.ThingWithDate = DS.Model.extend({
  startedAtMonth: DS.attr('number'),
  startedAtYear: DS.attr('number'),
  startedAt: dateComputed('startedAt'),
  
  endedAtMonth: DS.attr('number'),
  endedAtYear: DS.attr('number'),
  endedAt: dateComputed('endedAt')
});

model.rb

class ThingWithDate
  validates_numericality_of :started_at_month, :started_at_year, :ended_at_month, :ended_at_year,
    only_integer: true
end

serializer.rb

class ThingWithDateSerializer
  attribute :started_at_month, :started_at_year, :ended_at_month, :ended_at_year
end