On Tue, Mar 24, 2009 at 8:15 PM, Michael Glassford <glassfo...@gmail.com>wrote:
>
> Alex Gaynor wrote:
> >
> >
> > On Tue, Mar 24, 2009 at 2:51 PM, Michael Glassford wrote:
> >
> >
> > Alex Gaynor wrote:
> > >
> > >
> > > On Tue, Mar 24, 2009 at 2:39 PM, Michael Glassford wrote:
> >
> > [snip model definition, etc.]
> >
> > > When I run the tests under Django 0.96.3, I get the expected
> > exception:
> > > "DoesNotExist: ModelA matching query does not exist."
> > >
> > > However, under Django 1.0, 1.0.1, 1.0.2, and the current
> > trunk (revision
> > > 10162 at the time when I tested this), the
> > "ModelA.objects.get(pk=None)"
> > > statement unexpectedly returns the object created by the
> > > "ModelA.objects.create()" on the previous line.
> > >
> > >
> > > Mike
> > >
> > >
> > >
> > >
> > > Under MySQL doing a query of the form WHERE primary_key IS NULL
> > returns
> > > the last created row.
> > >
> > > Alex
> >
> >
> >
> > Not here:
> >
> > mysql> show create table myapp_modela;
> >
> +--------------+----------------------------------------------------------------------------------------------------------------------------------+
> > | Table | Create Table
> >
> > |
> >
> +--------------+----------------------------------------------------------------------------------------------------------------------------------+
> > | myapp_modela | CREATE TABLE `myapp_modela` (
> > `id` int(11) NOT NULL auto_increment,
> > PRIMARY KEY (`id`)
> > ) ENGINE=InnoDB DEFAULT CHARSET=utf8 |
> >
> +--------------+----------------------------------------------------------------------------------------------------------------------------------+
> > 1 row in set (0.00 sec)
> >
> > mysql> insert into myapp_modela values (1);
> > Query OK, 1 row affected (0.00 sec)
> >
> > mysql> select * from myapp_modela where id is NULL;
> > Empty set (0.00 sec)
> >
> >
> >
> > Also, that doesn't explain why Django 0.96 does what I expected.
> >
> >
> >
> > I'm almost positive the MySQL CLI operates differently for the purposes
> > of this query. The reason the queries do different things in .96 is
> > that in .96 that query becomes id = NULL rather than id IS NULL, which
> > MySQL handles differently.
>
>
> After more research, it turns out that my example doesn't display the
> problem because it isn't testing for the right thing. The actual
> behavior that MySQL implements is to return the last row inserted using
> an auto-increment id (which the above did not, since I supplied the id).
> Changing the example accordingly:
>
> mysql> insert into myapp_modela values();
> Query OK, 1 row affected (0.00 sec)
>
> mysql> select * from myapp_modela where id is null;
> +----+
> | id |
> +----+
> | 6 |
> +----+
> 1 row in set (0.00 sec)
>
>
>
>
> However, this behavior can be turned off:
>
> mysql> set sql_auto_is_null = 0; #Turn off using session variable
> Query OK, 0 rows affected (0.00 sec)
>
> mysql> insert into myapp_modela values();
> Query OK, 1 row affected (0.00 sec)
>
> mysql> select * from myapp_modela where id is null;
> Empty set (0.00 sec)
>
>
>
>
> Django can be patched to do this automatically. There may be a better
> way to do it, but I've figured out that in db/backends/mysql/base.py,
> inside the DatabaseWrapper._cursor function, adding the line
> "cursor.execute('SET sql_auto_is_null=0;')" immediately after the
> "cursor = CursorWrapper(self.connection.cursor())" line will do it.
> Should I submit a patch or is this just something that's not going to be
> fixed?
>
>
>
> Mike
>
> >
>
I believe that was discussed and decided against when the original
discussion occured on django-developers, you'd have to find the original
thread to be certain though.
Alex
--
"I disapprove of what you say, but I will defend to the death your right to
say it." --Voltaire
"The people's good is the highest law."--Cicero
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