I''ve been reading about locking for ActiveRecord, but it seems a little vague to me. My situation is this: I have a controller that assigns jobs to people who are logged in. The basic code is: j = Job.find :first, :conditions => ''employee_id is null'' unless j.nil? j.employee = current_employee j.save end Of course, this can cause, and has caused a race condition. My temporary fix was to add :order => ''RAND()'', so that the possibility of a collision is reduced, but the possibility is still there. It seems the lock! might fix this, but I don''t understand what really happens here. If I lock! the record, what happens to the second employee that tries to pull the record and save it? Is there another method I should be looking at?
On Oct 15, 2:34 pm, stack <step...-4ZZzgxzkY5nprZlt/sZkLg@public.gmane.org> wrote:> > Of course, this can cause, and has caused a race condition. My > temporary fix was to add :order => ''RAND()'', so that the possibility > of a collision is reduced, but the possibility is still there. > > It seems the lock! might fix this, but I don''t understand what really > happens here. If I lock! the record, what happens to the second > employee that tries to pull the record and save it? >lock! is a database level lock (ie select ... for update). You get an exclusive lock on that row that lasts for the duration of the current transaction (corollary: if you do this outside a transaction it basically does nothing). If something else tries to read or update that row that attempt will block until the lock is released (or the thing waiting for the lock gets bored of waiting)> Is there another method I should be looking at?Rails'' optimistic locking may also be relevant Fred