> On 12 January 2016 at 13:26, Scott Hess <shess at google.com> wrote:
>
> > On Mon, Jan 11, 2016 at 9:12 PM, Felipe Gasper <felipe at felipegasper.com>
> > wrote:
> >
> > > On 11 Jan 2016 9:06 PM, Rowan Worth wrote:
> > >
> > >> * if it returns SQLITE_OK and zero rows, the schema hasn't been
> created
> > >> yet
> > >>
> > >
> > > Sure; however, by the time you do the next action it?s possible that
> > > something else will be creating the schema. This is the condition that
> > I?m trying to avoid.
Then just do:
set timeout to something
BEGIN IMMEDIATE
PRAGMA user_version;
if returned value is *not* the user/schema version you want make it so IN THIS
TRANSACTION
{
... create/update schema ...
PRAGMA user_version=x;
}
COMMIT;
This is race condition free and will even work with an existing database in WAL
mode ...
There is no need for all the complication -- it is really quite simple.
Rather than rely on the user_version, you could check anything you like. The
secret sauce is to do all the checking and updating INSIDE the single IMMEDIATE
transaction.
