Typed property handle
So far, generic database access has been discussed. In contrast to generic property handles, types property handles provide direct access to instance data in the context of a C++ class definition. Typed property handles are supported via template classes. Instead of referring to the selected instance in the property node, the application may directly refer to instance properties returned by the template class.
When using typed property handles, the system will not be informed about instance modifications and the application program has to signal updates explicitly. Moreover, no data conversion will be performed and has to be managed by the application program as well.
Another disadvantage is, that you must not define virtual functions for types used in typed property handles, since the ODABA instance factory does not create virtual function vectors.
Hence, we suggest always using generic property handles rather than typed property handles.
// using typed Property Handles
PI<Person> persons(obh, "Person::Persons", PI_Write");
while ( persons.Next() )
if ( persons.Get()->UpdateAge() )
persons.Modify();
// Update function as implemented in the Person Class
bool Person::UpdateAge() {
int old_age;
dbdt current;
current.SetDate();
age = birth_date.Year() - current_year;
return ( age != old_age);
}
// using generic property handles with update control
Property persons(os, "Person", PI_Write");
Property birth_date(&persons, "birth_date");
Property age(&persons, "age");
Date current;
int year = current.setDate().Year();
while ( persons.Next() )
age = year - birth_date.GetDate().Year();