gistfile1.rb

# using active record you can easily hit this common performance issue
#

  class Parent
    has_many :children
  end

  class Child
    belongs_to :parent
  end

# now this hits the db ***every*** time to find the child's parent
#
  Parent.find(42).children.each do |child|
    child.parent
  end



# we can fix this easily like so
#
  class Parent
    has_many :children
    alias_method '__children__', 'children'

    def children
      __children__
    ensure
      __children__.each{|child| child.parent = self}
    end
  end

# now this doesn't hit the db at ***all*** for each child
#
  Parent.find(42).children.each do |child|
    child.parent
  end




# if you have the 'redef' gem installed this is even more compact, just do
#
  class Parent
    has_many :children

    redef do
      def children
        returning(super){|children| children.each{|child| child.parent = self}}
      end
    end
  end

# again this doesn't hit the db at ***all*** for each child
#
  Parent.find(42).children.each do |child|
    child.parent
  end