Using Caché Objects - InterSystems Documentation

For example, the following returns a set of all the object ID values for the Sample.Person
class:
Set rset = ##class(%ResultSet).%New("Sample.Person:Extent")
Do rset.Execute()
While (rset.Next()) {
Write rset.Data("ID"),!
}
The Sample.Person extent include all instances of Sample.Person as well as its subclass
Sample.Employee. If you want to only see the instances of Sample.Employee (and its subclasses)
then use its Extent query:
Set rset = ##class(%ResultSet).%New("Sample.Employee:Extent")
Do rset.Execute()
While (rset.Next()) {
Write rset.Data("ID"),!
}
The Extent query is equivalent to the following SQL query:
SELECT %ID FROM Sample.Person
Storage Definitions and Storage Classes
Note that you cannot rely on the order in which ID values are returned using either of these
method: Caché may determine that it is more efficient to use an index that is ordered using
some other property value to satisfy this request. You can add an ORDER BY %ID clause
to your SQL query if you need to.
12.4 Storage Definitions and Storage Classes
The %Persistent class provides the high-level interface for storing and retrieving objects in
the database. The actual work of storing and loading objects is performed by what is called
a storage class.
Every persistent (and serial) object uses a storage class to generate the actual methods used
to store, load, and delete objects in a database. These internal methods are referred to the
Storage Interface. The Storage Interface includes methods such as %LoadData, %SaveData,
and %DeleteData. Applications never call these methods directly, instead they are called at
the appropriate time by the methods of the Persistence Interface (such as %OpenId and
%Save).
Using Caché Objects 109