has_many through but with one table?

Maybe I'm looking at this the wrong way and with that - hopefully someone can either suggest a simpler way or the right way.

I have a Quote model - for all intents and purposes, just say it has one attribute :price.

I want to be able to add the following self-referential attributes (which I *think* should be under a has_many, through)

Quotes has_many requotes through... something

When a quote is made it's attached to a specific job and locked. When a similar job comes in, I want to take the original quote, duplicate it and update it to match the specs of the new job; the old quote still intact and both having a knowledge of their "parent-child" relationship.

I've looked at Ryan Bates latest railscast on self referential relationships but that doesn't seem to solve the whole problem.

Say I have quote_id 3 which has been requoted 3 different times. I then go back and requote one of those, say quote #4.. (check the "hopefully understandable" chart below)

quote#3 =quote#4 ==quote#7 =quote#5 =quote#6

quote 3 has 3 children and its first child has a child.

now say I delete quote 4... quote 7 doesn't know who its proverbial daddy is. and quote 3 doesn't know it has any grandchildren. in theory, i'd like 3&7 to link up when the link between them breaks.

any takers on this one?

Well, it's true that #4 knows its original, but #3 only knows about the requotes by asking, in effect, "Hey, I'm #3. Which of you quotes are requotes from me?"

class Quote    belongs_to :original, :class_name => 'Quote'    has_many :requotes, :class_name => 'Quote', :foreign_key => :original

   def requoted?      !self.original.nil?    end

   def requote      raise "Oops! Can't requote an unsaved Quote" if self.new_record?      child = self.clone      child.original = self.id    end end

three = Quote.new(:price => 1.00) {|q| q.id = 3 } three.save four = three.requote; four.save five = three.requote; five.save six = three.requote; six.save seven = four.requote; seven.save

OK, now then, is four.destroy allowed? (meaning does the business thing exist in such a way that it is OK?)

You might want to have a before_destroy callback that prevents a quote from being removed if it has been requoted.

class Quote    before_destroy :ensure_no_requotes # placed earlier than the has_many

   protected    def ensure_no_requotes      self.requotes.empty?    end end

Alternatively, you could treat the chain of requotes as a linked-list and self.requotes.each {|r|r.original = self.original; r.save} in an after_destroy callback perhaps.


Rob Biedenharn http://agileconsultingllc.com Rob@AgileConsultingLLC.com