[web2py] Re: Lazy virtual fields - strange result!
After some thought, I'm really liking this design for virtual
fields... what if lazy/virtual fields were declared directly in
db.define_table()? Like so:
db.define_table('item',
Field('unit_price','double'),
Field('quantity','integer'),
VirtualField('total_price',
lambda self:
self.item.unit_price*self.item.quantity,
lazy=True))
It's so simple.
I still kinda feel like we might find better names than lazy/virtual
though. So here's a design I like even more:
db.define_table('item',
Field('unit_price','double'),
Field('quantity','integer'),
Method('total_price',
lambda self:
self.item.unit_price*self.item.quantity,
precompute=False))
`precompute' means "not lazy" and would default to false.
On Aug 25, 6:14 am, Massimo Di Pierro
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)
>
[web2py] Re: Lazy virtual fields - strange result!
I'm sorry, that was a doofus comment. Of course lambdas allow side-
effects! I wish mailing lists supported "delete."
On Aug 27, 1:08 pm, Michael Toomim wrote:
> 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
> 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 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
[web2py] Re: Lazy virtual fields - strange result!
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
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 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
Re: [web2py] Re: Lazy virtual fields - strange result!
I got:
Traceback (most recent call last):
...
db.item.lazy_total_price=Field.lazy(lambda
self:self.item.unit_price*self.item.quantity)
AttributeError: type object 'Field' has no attribute 'lazy'
Version 1.98.2 (2011-08-25 19:11:31)
Martin
2011/8/25 Massimo Di Pierro
> The nightly build or trunk.
>
> On Aug 25, 10:24 am, Martin Weissenboeck wrote:
> > Thank you. Which version of web2py? 1.98.2 does not know Field.lazy
> >
> > 2011/8/25 Massimo Di Pierro
> >
> >
> >
> >
> >
> >
> >
> > > 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 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
>
[web2py] Re: Lazy virtual fields - strange result!
The nightly build or trunk.
On Aug 25, 10:24 am, Martin Weissenboeck wrote:
> Thank you. Which version of web2py? 1.98.2 does not know Field.lazy
>
> 2011/8/25 Massimo Di Pierro
>
>
>
>
>
>
>
> > 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 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
Re: [web2py] Re: Lazy virtual fields - strange result!
Thank you. Which version of web2py? 1.98.2 does not know Field.lazy
2011/8/25 Massimo Di Pierro
> 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 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
>
[web2py] Re: Lazy virtual fields - strange result!
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 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
