Rails - Aug 2007 - activerecord: detect if an association attribute has changed

Hi,

just a quick question, cause so far I was nt able to find a nice and
clean solution.

Let s assume an apple belongs_to a tree.
Now I would like to be able to detect in the apple model that the tree
has changed.
I would like to be able to detect changes if either apple.tree_id or
apple.tree is changed.

Any ideas?

--
Volker


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MrBanabas-gM/Ye1E23mwN+BqQ9rBEUg@public.gmane.org wrote:
> Hi,
> 
> just a quick question, cause so far I was nt able to find a nice and
> clean solution.
> 
> Let s assume an apple belongs_to a tree.
> Now I would like to be able to detect in the apple model that the tree
> has changed.
> I would like to be able to detect changes if either apple.tree_id or
> apple.tree is changed.
> 
> Any ideas?
> 
> --
> Volker
This is not easy, but here is a hackish solution:

Turn on optimistic locking on the Tree model.  (see 
http://scriptedzen.blogspot.com/2007/08/optimistic-locking-in-rails-with-active.html
)  This will among other things give you a new integer field that will 
change every time the record is saved.  In the Apple model store the 
value of lock_version field.  You can then check if this value has 
changed and take appropriate action.  If I were doing this I would check 
when an Apple was loaded and then again when it''s saved.  This might 
also work with a magic timestamp field.

There is (to my knowledge) no way of knowing in real time when the Tree 
changes except by having the Tree itself call all the Apples that 
belong_to it when it saves. (Very time consuming)

John Miller

-- 
Posted via http://www.ruby-forum.com/.

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