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 > > --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "web2py Web Framework" group. To post to this group, send email to [email protected] To unsubscribe from this group, send email to [email protected] For more options, visit this group at http://groups.google.com/group/web2py?hl=en -~----------~----~----~----~------~----~------~--~---
