LastPayReport.rb

require 'ostruct'

class LastPayReport

  def initialize employees
    @employees = employees
  end

  def get_rows
    rows = []

    @employees.each do |employee|

      employee.compensations.last_two
      row = OpenStruct.new

      row.full_name = employee.full_name
      row.department = employee.department.nil? ? "" : employee.department.name
      row.job_title = employee.job_title.nil? ? "" : employee.job_title.name
      row.previous_pay = employee.compensations.last_two[1].nil? ? "" : employee.compensations.last_two[1].pay_rate.to_s << "/" <<  employee.compensations.last_two[1].pay_type.to_s
      row.current_pay = employee.compensations.last_two[0].nil? ? "" : employee.compensations.last_two[0].pay_rate.to_s << "/" <<  employee.compensations.last_two[0].pay_type.to_s
      row.change_date = employee.compensations.last_two[1].nil? ? "" : employee.compensations.last_two[0].date

      rows << row
    end
    rows
  end
end

можно переписать на map.

employee.job_title.try(:name)

and so on