Using Caché Objects - InterSystems Documentation

Attribute Properties
CAUTION:
Do not set the property equal to the empty string using open- and close-quotes
(""), as this can result in values that are not valid or errors.
This is particularly significant if the application is using an external interface,
such as Java.
7.5.2 Object-Valued Properties
An object-valued property is a reference to another object, either embedded or persistent. In
either case, the value of the property is an OREF while in memory. On disk, a reference to a
persistent object becomes an OID, while an embedded object becomes a single serialized
string containing all of the embedded object's properties.
For instance, if an object-valued property, Doc, is of the type Doctor (where Doctor is either
a persistent object or an embeddable object), the definition of Doc is:
Property Doc As Doctor;
7.5.3 Collection Properties
A collection property is one that contains a group (or collection) of individual elements, all
of the same type. To specify a collection property, place the collection type at the start of the
property definition. Caché supports two kinds of collections, called List and Array collections..
The property type determines the contents of the collection. For example, the following code
defines a Colors property which is a list collection of %String values:
// Property Colors As List Of %String;
Property Colors As List Of %String; // the current syntax
Similarly, Caché supports object collections, as in the following Doctors property which is
an Array of references to Doctor objects:
Property Doctors As Array Of Doctor;
When you create a collection, Caché gives it a set of methods through a collection object.
Caché includes several kinds of collection objects, each one designed to operate on a different
kind of collection:
Collection Objects
Type
Data type
Object (persistent or embedded)
Array property
%ArrayOfDataTypes
%ArrayOfObjects
List property
%ListOfDataTypes
%ListOfObjects
Using Caché Objects 51