Yes. The values of virtualfields are not stored in the database. They
are computed every time a record is extracted.
In the above case the values are computed when a record is inserted
and they are stored in the database. In RDBS this is not really a good
idea but you may need it in non relational DBs like GAE.
Massimo
On Dec 27, 5:30 pm, Mengu <whalb...@gmail.com> wrote:
> is there any difference with this and our virtualfields?
>
> On 28 Aralık, 00:39, mdipierro <mdipie...@cs.depaul.edu> wrote:
>
> > It was easy to add it to the current DAL (will work on GAE too)
>
> > massimo-di-pierros-macbook:web2py mdipierro$ python web2py.py -S
> > welcome>>> db=DAL('sqlite://storage.sqlite')
> > >>> db.define_table('a',Field('b'),Field('c',compute=lambda r:
> > >>> r['b'].lower()))
> > >>> db.a.insert(b='HELLO')
> > >>> for row in db(db.a.id>0).select(): print row.b, row.c
> > HELLO hello
> > >>> db(db.a.id>0).update(b='WORLD')
> > >>> for row in db(db.a.id>0).select(): print row.b, row.c
>
> > WORLD world
>
> > On Dec 27, 4:16 pm, mdipierro <mdipie...@cs.depaul.edu> wrote:
>
> > > This thread
>
> > >http://groups.google.com/group/google-appengine-python/browse_thread/...
>
> > > raises an interesting issue and proposes an interesting solution that
> > > works on GAE.
>
> > > Executive summary: In GAE you can define computed fields that are
> > > computed now when data is extracted but when data is stored and the
> > > computed fields are stored too. Why? Because you can use them to
> > > perform operation that would otherwise not be supported on GAE.
>
> > > It would be trivial to support this in web2py and make it cross-db.
> > > Basically all we need is a new field attribute that points to a
> > > function that computes the value of a field based on the values of the
> > > other fields. We already have this db.table.field.update and it can be
> > > a function.
>
> > > I think the new DAL should support this.
>
> > > Massimo
>
>
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