# How to understand callback and validate\_associated

**URL:** <https://www.ruby-forum.com/t/how-to-understand-callback-and-validate-associated/192462>\
**Category:** Rails\
**Created:** [July 30, 2010, 6:01pm UTC](https://www.ruby-forum.com/t/how-to-understand-callback-and-validate-associated/192462 "2010-07-30T18:01:28Z")\
**Posts on this page:** 8\
**Page:** 1

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**Author:** ![daociyiyou](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/0ea827/32.png) [@daociyiyou](https://www.ruby-forum.com/u/daociyiyou)\
**Post date:** [July 30, 2010, 6:01pm UTC](https://www.ruby-forum.com/t/how-to-understand-callback-and-validate-associated/192462/1 "2010-07-30T18:01:28Z")

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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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**Author:** ![daociyiyou](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/0ea827/32.png) [@daociyiyou](https://www.ruby-forum.com/u/daociyiyou)\
**Post date:** [July 31, 2010, 3:41am UTC](https://www.ruby-forum.com/t/how-to-understand-callback-and-validate-associated/192462/2 "2010-07-31T03:41:27Z")

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anyone help me?

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<div class="post-metadata">

**Author:** ![daociyiyou](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/0ea827/32.png) [@daociyiyou](https://www.ruby-forum.com/u/daociyiyou)\
**Post date:** [July 31, 2010, 9:00am UTC](https://www.ruby-forum.com/t/how-to-understand-callback-and-validate-associated/192462/3 "2010-07-31T09:00:28Z")

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hi  
who know about it? thanks!

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**Author:** ![daociyiyou](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/0ea827/32.png) [@daociyiyou](https://www.ruby-forum.com/u/daociyiyou)\
**Post date:** [July 31, 2010, 11:48am UTC](https://www.ruby-forum.com/t/how-to-understand-callback-and-validate-associated/192462/4 "2010-07-31T11:48:04Z")

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On Jul 31, 8:00 am, Guo Y. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) 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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**Author:** ![daociyiyou](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/0ea827/32.png) [@daociyiyou](https://www.ruby-forum.com/u/daociyiyou)\
**Post date:** [July 31, 2010, 4:43pm UTC](https://www.ruby-forum.com/t/how-to-understand-callback-and-validate-associated/192462/5 "2010-07-31T16:43:47Z")

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

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<div class="post-metadata">

**Author:** ![daociyiyou](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/0ea827/32.png) [@daociyiyou](https://www.ruby-forum.com/u/daociyiyou)\
**Post date:** [July 31, 2010, 12:49pm UTC](https://www.ruby-forum.com/t/how-to-understand-callback-and-validate-associated/192462/6 "2010-07-31T12:49:20Z")

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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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<div class="post-metadata">

**Author:** ![daociyiyou](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/0ea827/32.png) [@daociyiyou](https://www.ruby-forum.com/u/daociyiyou)\
**Post date:** [August 1, 2010, 12:31am UTC](https://www.ruby-forum.com/t/how-to-understand-callback-and-validate-associated/192462/7 "2010-08-01T00:31:54Z")

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On Jul 31, 11:49 am, Guo Y. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) 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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<div class="post-metadata">

**Author:** ![daociyiyou](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/0ea827/32.png) [@daociyiyou](https://www.ruby-forum.com/u/daociyiyou)\
**Post date:** [August 1, 2010, 4:07am UTC](https://www.ruby-forum.com/t/how-to-understand-callback-and-validate-associated/192462/8 "2010-08-01T04:07:19Z")

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Thanks,fred.