[Dbix-class] Optimistic locking

[Matt S Trout]

Dan Horne wrote:
>> On Behalf Of Zbigniew Lukasiak
>>
>> Hi,
>>
>> There will be race conditions - is that acceptable for you?  See following
> scenario:
>> Person A wants to save new record values
>> Person B wants to save new record values
>> A fetches the record to compute the hash
>> B fetches the record to compute the hash
>> The record has not been changed yet so both A and B are ready to save
> their new values
>> A saves her new values
>> B saves her new values
>>
>> The result is that the values saved by A are overwritten by B without any
> warning.
>> It would be safe if we could do a
>>
>> UPDATE rec ... WHERE (id = our_id AND hash = the_old_hash_val)
>>
>> This would be a real optimistic locking using the database mechanisms to
> eliminate the race conditions.
>> --
>> Zbyszek
>>
> Yes, I've been thinking about this in the meantime and have decided to add a
> version column to each table and do something similar to what you suggested
> 
> UPDATE rec set col1 = <col1>, col2 = <col2> ... version = version + 1 ...
> WHERE conditions and version = old_version_value

If you're doing that, can you bear in mind that it'd rock if we could extend 
that later to add change auditing please? :)

(I was going to implement that but the project I needed it for got cancelled 
so it's gone onto the back-burner for the mo)