class UniqueIndexOnProfile < ActiveRecord::Migration
  class Profile < ActiveRecord::Base; end
  def self.up
    if Profile.count > 0
      conn = ActiveRecord::Base.connection
      columns = conn.columns("profiles").map{|c| c.name}
      ["id", "created_at", "updated_at"].each{|n| columns.delete(n)}

      sql = <<-SQL
      SELECT profiles.person_id FROM profiles
        GROUP BY #{columns.join(',')}
          HAVING COUNT(*)>1 AND profiles.person_id IS NOT NULL;
      SQL
      result = conn.execute(sql)
      duplicate_person_ids = result.to_a.flatten

      undesired_profile_ids = []
      duplicate_person_ids.each do |person_id|
        profile_ids = conn.execute("
          SELECT profiles.id FROM profiles
          WHERE profiles.person_id = #{person_id};").to_a.flatten
        profile_ids.pop
        undesired_profile_ids.concat(profile_ids)
      end
      conn.execute("DELETE FROM profiles
        WHERE profiles.id IN (#{undesired_profile_ids.join(",")});") unless undesired_profile_ids.empty?
    end

    remove_index :profiles, :person_id
    add_index    :profiles, :person_id, :unique => true
  end

  def self.down
    remove_index :profiles, :person_id
    add_index    :profiles, :person_id
  end
end