Thanks Christophe and Kenneth!
Let me make sure I understand this:
If I write this vew function:
@transaction.commit_on_success
def update_high_bid(request):
....
cursor = connection.cursor()
cursor.execute("SELECT high_bid FROM auctionapp_auction WHERE
id=%s
FOR UPDATE", [auction.id])
returned_rows = cursor.fetchall()
high_bid = returned_rows[0][0]
if new_bid > high_bid:
auction.high_bid = new_bid
auction.save()
The entire function will be wrapped within a transaction.
SELECT FOR UPDATE will acquire a row-level lock
and that lock will not be released until the function update_high_bid
() returns successfully, or until the function raises an exception and
the whole transaction is rolled back.
Is that right?
Thanks.
On Nov 10, 12:45 am, Christophe Pettus <x...@thebuild.com> wrote:
> On Nov 9, 2009, at 9:34 PM, Continuation wrote:
>
> > Also does django middleware acquire database lock on my behalf, or do
> > I need to explicitly perform the locking?
>
> In the example code, it's the SELECT ... FOR UPDATE that acquires the
> lock. Django doesn't currently have any explicit knowledge of
> locking, so you need to drop down to the custom SQL level to issue the
> right statement to acquire the lock on the row.
>
> The example I wrote assumed you were using PostgreSQL as the backend;
> you can get all sorts of details about locking in PostgreSQL here:
>
>
> http://www.postgresql.org/docs/8.4/interactive/explicit-locking.html#...
> --
> -- Christophe Pettus
> x...@thebuild.com
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