let me think about this...
On Jan 9, 6:20 pm, Robin B <[email protected]> wrote:
> > row.update_record(count=db.table.count+1)
>
> Nice, thats great syntax for incrementing counters, but you would need
> a lambda to do anything more complicated than arithmetic in a
> transaction.
>
> What about a more complex transaction like read a value and set it
> based on rules (for creating a lock)? That could only be accomplished
> with a lambda...right?
>
> Robin
>
> On Jan 9, 5:51 pm, mdipierro <[email protected]> wrote:
>
> > I think we have something like this without introducing a special
> > syntax for GAE based on lambda. In fact on non-gae you can now do
>
> > row.update_record(count=db.table.count+1)
>
> > The same could work on GAE with your code below.
>
> > massimo
>
> > On Jan 9, 1:11 pm, Robin B <[email protected]> wrote:
>
> > > To perform certain actions on GAE you need transactions, eg.
> > > atomically increment a counter.
>
> > > This is what it would look like:
>
> > > row.update_record(count=lambda r: r.count+1)
>
> > > The GAE driver would check attributes for lambdas and invoke a
> > > transaction when a lambda is present, the other SQL drivers could be
> > > modified to be tolerant of lambdas and pass the current row into the
> > > lambda and will get the correct outcome.
>
> > > The transaction would work something like this in gql.py:
>
> > > from google.appengine.ext import db as google_db
>
> > > def update_record_txn(attrs,table_obj):
> > > record = table_obj.get_by_id(attrs.id)
> > > for k,v in attrs:
> > > if isinstance(v,lambda x: x):
> > > v = v(record)
> > > setattr(record,k,v)
> > > record.put()
> > > return record
>
> > > try:
> > > return google_db.run_in_transaction(update_record_txn,
> > > row,table_obj)
> > > except:
> > > pass
> > > # could handle TransactionFailedError() caused by contention
>
> > > This would be backwards compatible.
>
> > > Thoughts?
>
> > > Robin
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