3.rb

class MarkProductExportsWhichMeetAllRequirements < ActiveRecord::Migration

  class Export < ActiveRecord::Base
    attr_accessible :meets_requirements
    
    self.inheritance_column = nil

    def meets_all_requirements?
      # Do some complex business logic which cannot be expressed via sql query
    end
  end

  def up
    Export.where(type: 'ProductExport').find_each do |product_export|
      product_export.update_attributes!(meets_requirements: product_export.meets_all_requirements?) 
    end
  end

  def down
    # ...
  end
end