Interesting approach to use lambdas. Since lambdas don't do side-
effects, I checked out my virtualfields to see if my uses have side
effects.
In my app I have:
12 methods total across 3 database tables
10 of those methods have no side-effects
2 have side-effects
The two methods with side-effects are:
1. row.delete() ... deletes the relevant rows in related tables
2. row.toggle_x() ... toggles the boolean field of x and updates
cached data on other tables and sends email notifications
Perhaps this information is useful in designing the next lazy
virtualfields.
On Aug 25, 9:14 pm, Massimo Di Pierro <massimo.dipie...@gmail.com>
wrote:
> We are moving away from this because of many problems. Try this
> instead. It is still experimental but may go into stable soon.
>
> def vfields():
> db.define_table('item',
> Field('unit_price','double'),
> Field('quantity','integer'))
> db(db.item.id>0).delete()
>
> db.item.lazy_total_price=Field.lazy(lambda
> self:self.item.unit_price*self.item.quantity)
>
> db.item.bulk_insert([{'unit_price':12.00, 'quantity': 15},
> {'unit_price':10.00, 'quantity': 99},
> {'unit_price':120.00, 'quantity': 2},])
> res = []
> for r in db(db.item.id>0).select():
> res.append([r.unit_price, r.quantity, r.lazy_total_price()])
> return dict(res=res)
>
> On Aug 25, 7:50 am, Martin Weissenboeck <mweis...@gmail.com> wrote:
>
>
>
>
>
>
>
> > I wanted to learn more about lazy virtual fields and therefore I have
> > repeated the example from the book:
>
> > def vfields():
> > db.define_table('item',
> > Field('unit_price','double'),
> > Field('quantity','integer'))
>
> > db(db.item.id>0).delete()
>
> > class MyVirtualFields:
> > def lazy_total_price(self):
> > return lambda self=self: self.item.unit_price*self.item.quantity
>
> > db.item.virtualfields.append (MyVirtualFields())
>
> > db.item.bulk_insert([{'unit_price':12.00, 'quantity': 15},
> > {'unit_price':10.00, 'quantity': 99},
> > {'unit_price':120.00, 'quantity': 2},])
>
> > res = []
> > for r in db(db.item.id>0).select():
> > res.append([r.unit_price, r.quantity, r.lazy_total_price()])
> > return dict(res=res)
>
> > The expected output is:
> > [[12.0, 15, 180.0], [10.0, 99, 990.0], [120.0, 2, 240.0]]
>
> > But I got
> > * [[12.0, 15, *240.0]*, [10.0, 99, *240.0*], [120.0, 2, 240.0]]*
> > *
> > *
> > *Three times the same result.
> > *
> > I have read the book and my program over and over again - but I cannot see
> > any error.*
> > *
>
> > Does somebody have an idea?
> > Martin
