Rails - Aug 2006 - Database transactions

Hello,

I have an application where I need to create two records in a database 
transaction.

ie:

  begin
    User.transaction(user) do
      User_details.transaction(user_details) do
        user.save
        user_details.save
      end
    end
  end

  rescue
    flash[:notice] "Insert rolled back... but why..??"
  end

>From reading the Agile book, I gather that once I wrap the request in a 
transaction I loose the validation state, so I have no easy what of 
knowing what went wrong.

I am just wonder what the best practise is..??

Is this something people would recommend?

user.validate
if user.errors.count == 0
   user_details.validate
   if user_details.errors.count == 0
      perform transaction_routine(user, user_details)
   end
end

rgds,
- matt.

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

On Aug 8, 2006, at 8:14 AM, Matt Stone wrote:

Not clear on your actual problem, but you could
simplify the code as below. As written, I''m not
sure that rescue clause was valid at all.
> I have an application where I need to create two records in a database
> transaction.
>
>   begin
>     User.transaction(user,user_details) do
>       user.save!
>       user_details.save!
>     end
>   rescue
>     flash[:notice] "Insert rolled back... but why..??"
>   end
-- 
-- Tom Mornini

On Aug 8, 2006, at 8:14 AM, Matt Stone wrote:
> I have an application where I need to create two records in a database
> transaction.
>
>   begin
>     User.transaction(user) do
>       User_details.transaction(user_details) do
>         user.save
>         user_details.save
>       end
>     end
>   end
>
>   rescue
>     flash[:notice] "Insert rolled back... but why..??"
>   end
>
>
>> From reading the Agile book, I gather that once I wrap the request  
>> in a
> transaction I loose the validation state, so I have no easy what of
> knowing what went wrong.
>
> I am just wonder what the best practise is..??
>
> Is this something people would recommend?
>
> user.validate
> if user.errors.count == 0
>    user_details.validate
>    if user_details.errors.count == 0
>       perform transaction_routine(user, user_details)
>    end
> end
(Transactions are per database connection, not per class or object,  
so you only need to call it once - the transaction method is  
available on all of them for convenience.)

def update
   User.transaction do
     @user.save!
     @user_details.save!
   end
rescue ActiveRecord::RecordInvalid
   flash.now[:error] = "error saving #{@user.name}"
   render :action => ''edit''
end

<%= error_messages_for ''user'' %>
<%= error_messages_for ''user_details'' %>

Though it''s likely more appropriate to manage this in your model,  
particularly if one object is dependent on the other.

jeremy

On 8 Aug 2006, at 16:14, Matt Stone wrote:
> Hello,
>
> I have an application where I need to create two records in a database
> transaction.
>
> ie:
>
>   begin
>     User.transaction(user) do
>       User_details.transaction(user_details) do
>         user.save
>         user_details.save
>       end
>     end
>   end
>
>   rescue
>     flash[:notice] "Insert rolled back... but why..??"
>   end
>
>
>> From reading the Agile book, I gather that once I wrap the request  
>> in a
> transaction I loose the validation state, so I have no easy what of
> knowing what went wrong.
You only lose the validation if you also have the transaction roll  
back the active record object as well as the database.

If you do this:
>
> begin
>     User.transaction(user) do
Use.transaction do
>       User_details.transaction(user_details) do
>         user.save
You probably want to do
user.save! here
The transaction aborts if an exception is thrown, not if the save  
fails. So you need to use save! to get the RecordInvalid exception  
thrown out.
>         user_details.save
>       end
>     end
>   end
>
>   rescue
user has not been rolled back, so contains all the errors from when  
it was saved
>     flash[:notice] "Insert rolled back... but why..??"
>   end
>
> Is this something people would recommend?
>
> user.validate
> if user.errors.count == 0
>    user_details.validate
>    if user_details.errors.count == 0
>       perform transaction_routine(user, user_details)
>    end
> end
Use the transaction if you need thread-safety (you don''t need thread  
safety if you are only serving with a single process, but that  
doesn''t mean it''s not worth thinking about upfront). The
transaction
in itself won''t magically make things threadsafe though; you need to  
think carefully about your failure scenarios and whether all of them  
cause an exception. For example, your case above creates a user  
record, then a user_details record. Suppose a separate thread updates  
the user record before the user_details record has been saved. Is  
this a problem?

Ben

-- 
Ben Blaukopf - Director
Airsource Ltd
Tel: 01223 708370 / 07786 916043