perhaps I'm missing something but wouldn't you just change the update() here to
all(), so that you SELECT only those rows you care about into memory, then
change each "foo" as needed and flush? I'm not seeing what the issue is. The
row isn't locked if you aren't using SELECT..FOR UPDATE.
On Apr 23, 2014, at 8:27 PM, Tim Kersten <t...@io41.com> wrote:
> I'd like to run a data migration on a live server, but only update rows if
> the data hasn't changed since I've read it, and would like to do so
> optimistically, so without locking the row. Doing so like below works and
> prevents me updating rows that have changed since I last read the row.
>
> Session.query(MyModel).filter_by(foo=old_foo_value).filter_by(bar=old_bar_value).update({'foo':
> new_foo_value})
>
> While the approach works, it doesn't use the ORM. (I use an after_flush hook
> to inspect & log changes from dirty instances in the session).
>
> Is there a way to update an ORM instance conditionally like above?
>
> Kindest Regards,
> Tim
>
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