Notice that Virtualfields do not need any knowledge of the db object.
You can declare the class in a module (not model).
Import the module and then apply them to the tables that need them.
On Aug 19, 6:03 pm, Massimo Di Pierro <massimo.dipie...@gmail.com>
wrote:
> You asked for it so here they are: built-in lazy virtual fields.
>
> Q. How do they work?
>
> A. Like normal virtual fields but no need to mess up with lambdas,
> etc. Just add a @staticmethod decorator. Here is an example:
>
> db=DAL()
> db.define_table('x',Field('number','integer'))
> if db(db.x).isempty(): [db.x.insert(number=i) for i in range(10)]
>
> class MyVirtualFields(object):
>
> # normal virtual
> field
> def normal_shift(self): return self.x.number+1
>
> # lazy virtual field (because of
> @staticmethod)
> @staticmethod
> def lazy_shift(self,delta=4): return self.x.number+delta
>
> db.x.virtualfields.append(MyVirtualFields())
>
> for row in db(db.x).select():
> print row.number, row.normal_shift, row.lazy_shift(delta=7)
>
> normal_shift is a normal virtual field
> lazy_shift is a lazy virtual field (the name is accidental, you can
> use any names of course).
>
> There is a conceptual difference. In the former case self.x is
> <instance>.<attribute> while in the latter self.x is <row>.<attribute>
> as there is no instance needed.
>
> This should be faster that some of the hacks we have attempted in the
> past and should not consume more memory than needed. There are no
> copies of objects when using only virtual fields.
>
> Enjoy!
