Thanks, Tom. That does help.
On Wednesday, September 5, 2012 6:02:27 AM UTC-4, Tom Evans wrote:
>
> On Wed, Sep 5, 2012 at 1:45 AM, Yo-Yo Ma <baxters...@gmail.com<javascript:>>
> wrote:
> > restaurant =
> >
> Restaurant.objects.select_for_update().select_related('owner').get(name=u'Koala
>
>
> > Kafe')
> >
> > Assuming the ``owner`` field points to a ``Person`` table, will the
> > aforementioned query prevent the ``Person`` row returned for the Koala
> > Kafe's owner from being saved in a separate transaction?
> >
> > (I will be using Postgres and using ``transaction.commit_on_success``)
> >
>
> select_for_update() …
>
> "Returns a queryset that will lock rows until the end of the
> transaction, generating a SELECT ... FOR UPDATE SQL statement on
> supported databases."
>
> Postgresql handles this …
>
> "If specific tables are named in FOR UPDATE or FOR SHARE, then only
> rows coming from those tables are locked; any other tables used in the
> SELECT are simply read as usual. A FOR UPDATE or FOR SHARE clause
> without a table list affects all tables used in the statement. If FOR
> UPDATE or FOR SHARE is applied to a view or sub-query, it affects all
> tables used in the view or sub-query."
>
>
> http://www.postgresql.org/docs/9.0/static/sql-select.html#SQL-FOR-UPDATE-SHARE
>
>
> Django doesn't specify any tables when it generates a SELECT … FOR UPDATE
> query:
>
>
> https://github.com/django/django/blob/master/django/db/backends/__init__.py#L585
>
>
> Hope that helps
>
> Tom
>
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