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)

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"

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 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?

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

three = Quote.new(:price => 1.00) {|q| q.id = 3 }
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

   def ensure_no_requotes

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