Rails - Mar 2007 - Selective optimistic locking

I''m working on a photo gallery and use optimistic locking to prevent
concurrent editing of photo description.
At the same time I want to gather view statistics, incrementing a
counter every time a user views a larger version of a photo.

There are two solutions that came to my mind:

- split photo into two models: description and statistics,
- update view count without increasing lock_version.

The first one is a bit troublesome (I''d need to maintain a real 1 : 1
relationship, not a 1 : 0 .. 1), so I decided to implement the second.

My problem is that there''s no easy and _documented_ way to do this.
Here''s my solution:

(in the Photo model)
  def increment_view_count!
    Photo.transaction do
      lock!
      # optimistic lock must by turned off for this update
      increment(:views)
      update_without_lock
    end
  end

update_without_lock is defined in ActiveRecord::Locking::Optimistic,
it''s an alias to original update from ActiveRecord::Base, afaik.

This allows a privileged user to edit a photo and others may increase
the view count at the same time.

Could you comment on this? Maybe you have some other ideas?
--
Marcin Simonides

-- 
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Marcin Simonides wrote:
>   def increment_view_count!
>     Photo.transaction do
>       lock!
>       # optimistic lock must by turned off for this update
>       increment(:views)
>       update_without_lock
>     end
>   end
If you don''t need to read the current view count when
incrementing, an alternative is:

def increment_view_count!
   Photo.increment_counter(:views, id)
end

-- 
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Mark Reginald James wrote:
> Marcin Simonides wrote:
> 
>>   def increment_view_count!
>>     Photo.transaction do
>>       lock!
>>       # optimistic lock must by turned off for this update
>>       increment(:views)
>>       update_without_lock
>>     end
>>   end
> 
> If you don''t need to read the current view count when
> incrementing, an alternative is:
> 
> def increment_view_count!
>    Photo.increment_counter(:views, id)
> end
Good point, thanks.

--
Marcin Simonides

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

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