The [ DBTable ] attribute controls where class instances are
persisted. The domain class attributed with [ DBTable ] and
all their children get their own class. This mechanism is
explained briefly here: FIXME, a more comprehensive discussion
is the section FIXME in the PhoneBook tutorial.
For this PhoneBook sample, our hierarchy is boring – no subclassing
of domain object classes here. We give each class it's own [ DBTable ]
attribute, thus its own table:
...
We don't have many options here, but an alternative would be to
introduce an abstract base type PhoneBookBase, derive all
PhoneBook domain classes from it and persist them all in the same
table:
As you see, the three sub-classes inherit the DBTable
attribute from abstract PhoneBookBase class. They share
a DBTable attribute, so they share a table. The column
names are merged. For this scenario it is useful to have that
{{DBColumn}}mentioned above, by the way. Without it, we would get column name clashes, because both the {{Location class
has a property Number, but also the PhoneNumber class.