You make a good point. The code must be revised to take care of this situation. I need to think about it.
On Nov 18, 8:20 am, VijayS <[email protected]> wrote: > Hello, > > I am new to web2py, and this group. I was conversing on IRC and it > was suggested by dingding1 that I should post this here. > > I think there's a bug with virtualfields. It seems that if I try to > use a select() statement with only one field name, then virtualfields > will fail to work as it cannot find the other dependent fields it > needs to calculate the desired output. > > So if this is desired behavior, it is not mentioned in the book (3rd > ed), and it seems to be counter intuitve as it seems like the > virtualclass should have access to all elements regardless of the > select query being run on it. > > see following example codehttp://pastie.textmate.org/1308330 > > class MyVirtualFields(object): > def production_total(self): > return > self.production.production_shift_1+self.production.production_shift_2+self.production.production_shift_3 > def production_net(self): > return > self.production.production_shift_1+self.production.production_shift_2+self.production.production_shift_3- > self.production.production_rejection > def lid_total(self): > return > self.production.lid_shift_1+self.production.lid_shift_2+self.production.lid_shift_3 > #NOTE virtual fields cause a problem with SELCT() statements. In the > select statement if you don't include the required fields for the > calculation, it will give an error! This is a bug! > #crashes on the following query > # rows = db(db.production.date_id == > date.today()).select(db.production.delivered) > #if i comment our the select criteria as shown below, then it works > fine > # rows = db(db.production.date_id == > date.today()).select()#db.production.delivered) > db.production.virtualfields.append(MyVirtualFields()) > > is this a valid, or just flawed understanding on my part? > maybe it makes sense to not have virtualfields access to all fields, > because that would mean fetching all data from server all the time, > thereby slowing down. > but then it should allow a switch for disabling it's evaluation or > something so that when running code that doesn't require the > virtualfield then it can skip the evaluation. > > Thank you for your patience. > > Vijay
