On Nov 15, 2007, at 1:40 PM, Ronald Lew wrote:
>
> I am having issues creating a read-only column using column_property.
> I have a phone table that has the columns: id, country_code, number,
> and deleted. I want to have an international column which will be set
> to True or False (or 1 or 0) depending on the value of the
> country_code. Provided below is the snippet of code to work with:
>
> phone_table = Table('phones', metadata,
> Column('id', Integer, primary_key=True),
> Column('country_code', String(5)),
> Column('number', String(20)),
> Column('deleted', Boolean, default=False),
> )
>
> class Phone(object):
> pass
>
> # international gets set to True or None which isn't intended
> # also the session is from turbogears.database import session
> session.mapper(Phone, phone_table, properties={
>
> 'international
> ':column_property
> ((phone_table.c.country_code=='1').label('international'))
> })
>
>
>
> I'm not sure if this is a Turbogears issue or SQLAlchemy issue but the
> international field is always None when I do the following: I
> instantiate a Phone object, populate the attributes, session.save the
> instantiated Phone object, session.flush, and then query the new Phone
> object.
this wont work unless you refreshed or expired the instance, or
expired the individual instance attribute (which is a feature we will
have in an upcoming release, although i can show you the non-public
way to do it right now if you were interested). SA has no idea
otherwise that it should reload the "international" attribute after a
flush().
however, a much better way to do it which doesnt require an additional
SELECT issued to the database would be a straight property:
class Phone(object):
def international(self):
return self.country_code == 1
international = property(international)
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