how would it be implemented if it does not know which record to lock?
On Jan 10, 6:53 pm, Robin B <[email protected]> wrote:
> What about:
>
> def my_txn(db):
> record = db(db.table.id==123).select()[0]
> record.update_record(count=record.count+1)
> return record.count
>
> count = db.transaction(my_txn)
>
> Robin
>
> On Jan 9, 9:44 pm, Robin B <[email protected]> wrote:
>
> > The next logical step is creating, reading, updating, and deleting
> > other records from within the transaction, at which point the lambda
> > which is really a function, should not be stuck under the field=...
> > since it is now much more than a field.
>
> > Since the lambda is passed the entire record, perhaps the syntax
> > should be more like:
>
> > def my_txn(record):
> > record = record.count+1
> > return record
>
> > row.update_record(my_txn)
>
> > the query checks if isinstance(obj,callable)...
>
> > Gotta run, Hasta Manana.
>
> > Robin
>
> > On Jan 9, 9:10 pm, mdipierro <[email protected]> wrote:
>
> > > The more I think about this the more I like your solution.
>
> > > We can provide both notations:
> > > 1) row.update_record(count=db.table.count+1)
> > > 2) row.update_record(count=lambda r: r.count+1)
> > > and the lambda notation should work even without GAE.
>
> > > If you send me the patch for GAE I can fix the non-gae.
>
> > > Massimo
>
> > > On Jan 9, 6:30 pm, mdipierro <[email protected]> wrote:
>
> > > > 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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