In real usage, is a user likely to be able to update the date field and
then quickly click the view link so fast that the view query happens before
the update query? If so, then your client side feedback idea is probably
the way to go.
Actually, if both the update and view requests use the session (or rather,
do not do session.forget), and you are using file based sessions, then the
first request should block the second request until the first request
completes. In that case, you could only get a race condition if the view
request actually arrives at the server before the update request.
Anthony
On Friday, December 9, 2011 11:43:37 AM UTC-5, Cliff wrote:
>
> The problem occurs in many-to-many relations, as in this example
> model:
>
> db.define_table('owners', Field('name'))
> db.define_table('dogs', Field('name'))
> db.define_table(dog_owners',
> Field('owner_id', db.owners),
> Field('dog_id', 'db.dogs'),
> Field('date_owner_got_dog', 'date') #This is important!
> )
>
> When an owner record is edited, I would also put on the page a table
> of all dogs owned by the owner. With each dog there is a field for
> editing date_owner_got_dog. The change event for that field triggers
> a jQuery script. The script uses Ajax to tell the server to update
> the value.
>
> When an owner record is viewed, I would put up the same table without
> capability to edit date_owner_got_dog.
>
> Here is how to get the race condition:
> 1. Open an owner record for editing.
> 2. Update one of date_owner_got_dog fields.
> 3. Quickly click the 'view' link.
> 4. Observe old value in the updated field because the server fetched
> the dog record before it was updated.
>
> The server can fetch the owner and dog records before finishing the
> update triggered by step 2.
>
> I didn't see this in manual testing but Selenium found it right away.
>
> I'm going to put up a 'please wait' flash message before kicking off
> the ajax call and change it to a 'done' message when the server has
> done its piece.
>
> Anybody have any better ideas?
>
> How does smartgrid handle this?
>
>
