# Transaction question - when does rails handle it itself?

**URL:** <https://www.ruby-forum.com/t/transaction-question-when-does-rails-handle-it-itself/68078>\
**Category:** Rails\
**Created:** [September 8, 2006, 11:37pm UTC](https://www.ruby-forum.com/t/transaction-question-when-does-rails-handle-it-itself/68078 "2006-09-08T23:37:54Z")\
**Posts on this page:** 5\
**Page:** 1

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**Author:** ![greg](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/g/71c47a/32.png) [@greg](https://www.ruby-forum.com/u/greg)\
**Post date:** [September 8, 2006, 11:37pm UTC](https://www.ruby-forum.com/t/transaction-question-when-does-rails-handle-it-itself/68078/1 "2006-09-08T23:37:54Z")

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Hi,

Can anyone confirm whether this is correct:

a) If you are an update to a model that has relations, rails  
automatically handles updating the relationship table as required and  
wraps everything itself in a transaction

b) If you are doing multiple updates within the same model =\> wrap a  
transaction around it yourself

c) If you are doing multiple updates across various models =\> wrap a  
transaction around it yourself (??is this correct??) and it will be  
handled

d) If you want to have your model objects (as well as database) accurate  
after a failure/rollback then list the object explicitly as parameters  
to the transaction( ) method. “Thereâ??s a downside to having the  
transaction code recover object state  
automaticallyâ??you canâ??t get to any error information added during  
validation” (from AWDR) ==\> QUESTION: Is this last point an issue? do  
people usually not worry about trying to get their model recovered  
correctly? i.e. as it would be re-generated with the next web request  
anyway?

Tks

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**Author:** ![greg](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/g/71c47a/32.png) [@greg](https://www.ruby-forum.com/u/greg)\
**Post date:** [September 9, 2006, 12:41am UTC](https://www.ruby-forum.com/t/transaction-question-when-does-rails-handle-it-itself/68078/2 "2006-09-09T00:41:17Z")

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> a) If you are an update to a model that has relations, rails  
> automatically handles updating the relationship table as required and  
> wraps everything itself in a transaction

Yes. Additionally, any SQL calls happening within a before or after  
filter will be governed by the automatic transaction.

> b) If you are doing multiple updates within the same model =\> wrap a  
> transaction around it yourself

Correct.

> c) If you are doing multiple updates across various models =\> wrap a  
> transaction around it yourself (??is this correct??) and it will be  
> handled

Correct.

> d) If you want to have your model objects (as well as database) accurate  
> after a failure/rollback then list the object explicitly as parameters  
> to the transaction( ) method. “There’s a downside to having the  
> transaction code recover object state  
> automatically-you can’t get to any error information added during  
> validation” (from AWDR) ==\> QUESTION: Is this last point an issue? do  
> people usually not worry about trying to get their model recovered  
> correctly? i.e. as it would be re-generated with the next web request  
> anyway?

Object transactions are going to be deprecated and remove by 2.0.  
There’s a variety of issues with them and they are very rarely used. If  
you still want them post-2.0, you can always add them in yourself. Or  
perhaps someone can wrap up a plugin to make it easy.

David Heinemeier H.

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<div class="post-metadata">

**Author:** ![greg](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/g/71c47a/32.png) [@greg](https://www.ruby-forum.com/u/greg)\
**Post date:** [September 9, 2006, 1:25am UTC](https://www.ruby-forum.com/t/transaction-question-when-does-rails-handle-it-itself/68078/3 "2006-09-09T01:25:21Z")

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On 9/8/06, Greg H. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote:

> Can anyone confirm whether this is correct:
> 
> a) If you are an update to a model that has relations, rails  
> automatically handles updating the relationship table as required and  
> wraps everything itself in a transaction

Yes.

b) If you are doing multiple updates within the same model =\> wrap a

> transaction around it yourself

Yes.

c) If you are doing multiple updates across various models =\> wrap a

> transaction around it yourself (??is this correct??) and it will be  
> handled

Yes.

d) If you want to have your model objects (as well as database) accurate

> after a failure/rollback then list the object explicitly as parameters  
> to the transaction( ) method. “There’s a downside to having the  
> transaction code recover object state  
> automaticallyâ??you can’t get to any error information added during  
> validation” (from AWDR) ==\> QUESTION: Is this last point an issue? do  
> people usually not worry about trying to get their model recovered  
> correctly? i.e. as it would be re-generated with the next web request  
> anyway?

You usually want the record in its dirty state so you can present the  
errors  
to the user. Object transactions are marginally useful and will be spun  
off  
into a plugin after Rails 1.2.

jeremy

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<div class="post-metadata">

**Author:** ![greg](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/g/71c47a/32.png) [@greg](https://www.ruby-forum.com/u/greg)\
**Post date:** [September 9, 2006, 3:01am UTC](https://www.ruby-forum.com/t/transaction-question-when-does-rails-handle-it-itself/68078/4 "2006-09-09T03:01:30Z")

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On 9/8/06, removed\_email\_address@domain.invalid [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote:

> In my experience, transactions belong at the application layer. J2EE  
> has taught much of the world that container managed transactions are a  
> bad (verging on evil) idea except in very small applications.

Active Record doesn’t do container-managed transactions. The destroy and  
save callback chains are wrapped in transactions. Otherwise, it’s all  
you.

Rollbacks should return the model objects to their state prior to the

> failed transaction, but the application should also gather whatever  
> information it can from the RDBMS about what caused the transaction to  
> fail.

Perhaps this would be sensible elsewhere, but in a typical web app you  
spit  
an error and the request is done. The database rollback is sufficient;  
fancy  
rollbacks are a roadblock.

In my experience, a failed transaction is either a symptom of

> inadequate pre-save edit checks, or a result of a blind dependency on a  
> program on another system that is identifiable at runtime, and should  
> be trapped so that a “plain english” error message can be delivered to  
> the user.

Active Record \<3 validation.

What is the proposed mechanism for giving the application control of

> the traqnsaction in Rails 2.0?

See the current mechanism and subtract object-level transactions.

jeremy

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<div class="post-metadata">

**Author:** ![greg](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/g/71c47a/32.png) [@greg](https://www.ruby-forum.com/u/greg)\
**Post date:** [September 9, 2006, 2:07am UTC](https://www.ruby-forum.com/t/transaction-question-when-does-rails-handle-it-itself/68078/5 "2006-09-09T02:07:25Z")

</div>

In my experience, transactions belong at the application layer. J2EE  
has taught much of the world that container managed transactions are a  
bad (verging on evil) idea except in very small applications.

Rollbacks should return the model objects to their state prior to the  
failed transaction, but the application should also gather whatever  
information it can from the RDBMS about what caused the transaction to  
fail.

In my experience, a failed transaction is either a symptom of  
inadequate pre-save edit checks, or a result of a blind dependency on a  
program on another system that is identifiable at runtime, and should  
be trapped so that a “plain english” error message can be delivered to  
the user.

What is the proposed mechanism for giving the application control of  
the traqnsaction in Rails 2.0?