Rails - Nov 2009 - atomic INSERT or UPDATE with activerecord

what i need:
if :record is in the database -> upgrade his counter
else create :record (with his counter on 1)

this should be done with an atomic operation, to avoid race
conditions.
What is the best way to do this with activerecord?
I read about transactions, but as i understand a transaction acts on a
single connection to the database.

On Nov 8, 10:41 am,
"eugenio.mode...-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org"
<eugenio.mode...-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
wrote:
> what i need:
> if :record is in the database -> upgrade his counter
> else create :record (with his counter on 1)
>
> this should be done with an atomic operation, to avoid race
> conditions.
> What is the best way to do this with activerecord?
> I read about transactions, but as i understand a transaction acts on a
> single connection to the database.
incrementing the counter is simple enough - AR''s increment_counter
method basically does update foos set counter = counter + 1 where ...

To avoid duplicate records being created I''d create a unique index on
whatever it is that identifies a record

Fred

eugenio.modesti-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org
wrote:
> what i need:
> if :record is in the database -> upgrade his counter
> else create :record (with his counter on 1)
> 
> this should be done with an atomic operation, to avoid race
> conditions.
> What is the best way to do this with activerecord?
> I read about transactions, but as i understand a transaction acts on a
> single connection to the database.
This would be a single DB connection, so it seems like a good candidate 
for a transaction.  What''s the problem with doing that?

Best,
--
Marnen Laibow-Koser
http://www.marnen.org
marnen-sbuyVjPbboAdnm+yROfE0A@public.gmane.org
-- 
Posted via http://www.ruby-forum.com/.

On Nov 8, 6:50 pm, Marnen Laibow-Koser <rails-mailing-l...@andreas-
s.net> wrote:
> This would be a single DB connection, so it seems like a good candidate
> for a transaction.  What''s the problem with doing that?
i think that multiple requests use multiple db connections, didn''t
they?  This is obviously true having two database server in a multi-
master configuration. I think that Frederick Cheung''s solution should
solve the problem anyway.
thank you.

eugenio wrote:
> On Nov 8, 6:50�pm, Marnen Laibow-Koser <rails-mailing-l...@andreas-
> s.net> wrote:
>> This would be a single DB connection, so it seems like a good candidate
>> for a transaction. �What''s the problem with doing that?
> i think that multiple requests use multiple db connections, didn''t
> they?  
Of course.  But you shouldn''t need a transaction over multiple
requests;
just encapsulating the INSERT and counter increment in a transaction, 
within a single request cycle, should do the trick.
> This is obviously true having two database server in a multi-
> master configuration.
Well, that''s just asking for trouble. :)
> I think that Frederick Cheung''s solution should
> solve the problem anyway.
> thank you.
Best,
--
Marnen Laibow-Koser
http://www.marnen.org
marnen-sbuyVjPbboAdnm+yROfE0A@public.gmane.org
-- 
Posted via http://www.ruby-forum.com/.