Re: [Sqlalchemy-tickets] [sqlalchemy] #2861: document use of version_id_col with versioning example (was: Hazard during versioning records)

[sqlalchemy <mi...@zz...>]

#2861: document use of version_id_col with versioning example
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      Reporter:  bikbit         |      Owner:  zzzeek
          Type:  defect         |     Status:  new
      Priority:  medium         |  Milestone:  0.9.0
     Component:  documentation  |   Severity:  trivial - <10 minutes
    Resolution:                 |   Keywords:  versioning
Progress State:  in queue       |
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Changes (by zzzeek):

 * milestone:  0.8.xx => 0.9.0
 * component:  utils => documentation
 * severity:  very major - up to 2 days => trivial - <10 minutes
 * status_field:  awaiting triage => in queue


Comment:

 sure, this is a natural effect of the two transactions not being entirely
 isolated.  If you have your isolation set at at least REPEATABLE READ then
 you wouldn't get this issue.

 you can alleviate this condition using a different kind of "versioning"
 which is the mapper-level versioning feature, see
 http://docs.sqlalchemy.org/en/rel_0_9/orm/mapper_config.html#configuring-a
 -version-counter.

 I've committed a proof of concept for this in rac54ba0f2d8df5a76b685284.
 A change could be to make this a flag on the `Versioned` class itself and
 to add documentation.

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Ticket URL: <http://www.sqlalchemy.org/trac/ticket/2861#comment:1>
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