N+1 problem

industry.rb

class Industry
  def initialize name, parent=nil
    @name, @parent = name, parent
  end

  def full_name
    [parent_name, @name].reject{|n| n.empty?}.join(' / ')
  end

  def parent_name
    @parent.nil? ? '' : @parent.full_name
  end
end

ind1 = Industry.new 'Name 1'
ind2 = Industry.new 'Name 2', ind1
ind3 = Industry.new 'Name 3', ind2

puts ind3.full_name  # => "Name 1 / Name 2 / Name 3"