Using Caché Objects - InterSystems Documentation

Object Persistence
// Open person "10"
Set obj = ##class(Sample.Person).%OpenId(10)
Write obj.%ClassName(),!
// Sample.Person
// Open person "110"
Set obj = ##class(Sample.Person).%OpenId(110)
Write obj.%ClassName(),!
// Sample.Employee
Note that the %OpenId method for the Sample.Employee class will not return an object if
we try to open ID 10:
// Open employee "10"
Set obj = ##class(Sample.Employee).%OpenId(10)
Write $IsObject(obj),! // 0
// Open employee "110"
Set obj = ##class(Sample.Employee).%OpenId(110)
Write $IsObject(obj),! // 1
This is because the %OpenId method for the Sample.Employee will only return instances
of Sample.Employee (or its subclasses). In the above example, 10 refers to an instance of
Sample.Person and cannot be opened as a Sample.Employee object.
For more information on polymorphism and persistent objects see the section on Extents.
12.2.2.2 Multiple Calls to %OpenId
If %OpenId is called multiple times within a Caché process for a specific persistent object
ID, only one object instance is created in memory: all subsequent calls to %OpenId will
return a reference to the object already loaded into memory.
This is demonstrated in the following example:
' open and modify Person 1 in memory
personA = OpenId Sample.Person(1)
personA.Name = "Black,Jimmy Carl"
' open Person 1 "again"
personB = OpenId Sample.Person(1)
PrintLn "NameA: " & personA.Name
PrintLn "NameB: " & personB.Name
12.2.2.3 Swizzling
If you open (load into memory) an instance of persistent object, and use a persistent object
it references, then this referenced object is automatically opened. This process is referred to
as swizzling.
104 Using Caché Objects