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 B. 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?

On Aug 20, 2009, at 11:58 PM, [email protected] wrote:

has_many requotes through… something
Say I have quote_id 3 which has been requoted 3 different times. I

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

Rob B. http://agileconsultingllc.com
[email protected]

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