Rails - Jul 2010 - how to understand callback and validate_associated

1 after_update callback is wrapped in transaction means:no matter
exception occurs during saving an existing record, or in the
after_update method body,both the existing record and record
manipulation in the after_update body are all rollbacked?

2  class Book < ActiveRecord::Base
    has_many :pages
    validates_associated :pages
    validates_presence_of :name
   end

validate_associated means: when i invoke book.save to save book and
it''s
associations,no matter invalidation occurs during saving book self or
saving any association,both book and all the associations don''t be
saved?

I don''t understand these from document.can you help me to make it sure?
Thanks!
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anyone help me?
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hi
  who know about it? thanks!
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On Jul 31, 8:00 am, Guo Yangguang
<li...-fsXkhYbjdPsEEoCn2XhGlw@public.gmane.org>
wrote:
> hi
>   who know about it? thanks!

Maybe you could rephrase your question - I for one couldn''t understand
what you were asking

Fred
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thank!
I copy the after_update() doc as following:
#######
after_update()

Is called after Base.save on existing objects that have a record. Note 
that this callback is still wrapped in the transaction around save. For 
example, if you invoke an external indexer at this point it won’t see 
the changes in the database.
########
I don''t understand "Note that this callback is still wrapped in
the
transaction around save".
if exception occurs when saving the existing record, or when executing
after_update method body,both the existing record''s saving and sql
statements in the after_update method body are all rollbacked?


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I have described the problem clearly.Can you help me?

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On Jul 31, 11:49 am, Guo Yangguang
<li...-fsXkhYbjdPsEEoCn2XhGlw@public.gmane.org>
wrote:
> ########
> I don''t understand "Note that this callback is still wrapped
in the
> transaction around save".
> if exception occurs when saving the existing record, or when executing
> after_update method body,both the existing record''s saving and sql
> statements in the after_update method body are all rollbacked?
>
Correct. The entirety of the save process (validations, before_save,
after_save etc.) is wrapped in a single transaction.

Fred

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Thanks,fred.

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