[Dbix-class] nested transactions and communicating to other processes

[Aran Deltac]

AFAIK there is no native way to make this situation easier, if thats what
you are hoping for.  You could make a stack on the engine object where you
could pop on things todo when a transaction is committed, and then modify
the commit sub to unpop and run the stack after commit.  Not sure how good
of a design that is, and makes a lot of action-at-a-distance, making things
a bit harder to debug and possibly introducing weird edge case issues.

Aran

On Thu, Oct 23, 2014 at 1:32 AM, Dami Laurent (PJ) <
laurent.dami at justice.ge.ch> wrote:

> Hi there,
>
> I encountered a delicate situation involving nested transactions.
> Consider a subroutine more or less like this :
>
>   sub insert_and_publish {
>     my @keys = $schema->txn_do(sub {some_complex_inserts()});
>     publish_to_outer_world(@keys);
>   }
>
> This creates a bunch of records within a transaction. If the transaction
> succeeds, changes are commited to the database, and then we can publish the
> record keys to other processes. With one single transaction, everything is
> well. However, if this is called from another transaction, we get into
> trouble :
>
>   $schema->txn_do(sub {
>     insert_and_publish();
>     do_some_more_stuff();
>    });
>    # only now did the real commit take place
>
> The problem here is that because of nested transactions, the commit only
> takes place at the outermost level; so the sequence of operations in
> insert_and_publish() no longer works : other processes get notified about
> keys that have not been committed yet (because do_some_more_stuf() might
> take some time), or possibly will never be committed (because
> do_some_more_stuf() might fail).
>
> The question is : how to rewrite insert_and_publish() so that it would
> work equally well in a single transaction, or in a nested transaction ? It
> seems that what is needed is a callback mechanism, to record things that
> should be done just after the transaction, and would be called
> automatically after commit time. Any suggestions ?
>
> Thanks in advance, Laurent Dami
>
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