Using Caché Objects - InterSystems Documentation

Object Persistence
1. Its primary (first) superclass must either be %Persistent or some other persistent class,
and,
2. It must specify that its ClassType is persistent.
For example:
Class MyApp.MyClass Extends %Persistent [ClassType = persistent]
{
}
If you omit the ClassType = persistent or if %Persistent (or a subclass) is not the first
class in the superclass list, then your class will not be persistent.
12.2 The Persistence Interface
The %Persistent class defines a set of methods, known as the Persistence Interface, that provides
the means to work with object persistence. Among other things, the Persistence Interface
provides the ability to save objects to the database, load objects from the database, delete
objects, and test for existence. These are described in the following sections.
12.2.1 Saving Objects
To save a persistent object to the database, invoke its %Save method:
Set obj = ##class(MyApp.MyClass).%New()
Set obj.MyValue = 10
Set sc = obj.%Save()
The %Save method returns a %Status value that indicates whether the save operation succeeded
or failed (such as if it has invalid property values or violates a uniqueness constraint).
Calling %Save on an object automatically saves all modified objects that can be “reached”
from the object being saved: that is, all embedded objects, collections, streams, referenced
objects, and relationships involving the object are automatically saved if needed. The entire
save operation is carried out as one transaction: if any object fails to save, then the entire
transaction fails and rolls back (no changes are made to disk; all in-memory object values
are what they were prior to calling %Save).
When an object is saved for the first time, the %Save method automatically assigns it an
Object ID value (the ID is generated using the $Increment function unless the class is using
a user-provided Object ID based on property values using an idkey index) that is used to later
100 Using Caché Objects