Rails - Aug 2009 - 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?

On Aug 20, 2009, at 11:58 PM,
frankjmattia-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org
wrote:
> 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

Rob Biedenharn		http://agileconsultingllc.com
Rob-xa9cJyRlE0mWcWVYNo9pwxS2lgjeYSpx@public.gmane.org