Using Caché Objects - InterSystems Documentation

14.4 Persistent Behavior of Relationships
Though there are two sides to every relationship, only one side actually has its relationshiprelated
information stored to disk. This is the single-valued side, the PARENT or ONE of
the relationship.
When you open an instance of the multi-valued side of a relationship, Caché treats its relationship
property as a standard object reference; it opens and swizzles into memory the
PARENT or ONE object. When you open an instance of the single-valued side of a relationship,
Caché uses a query to locate and create a list of all the relevant CHILDREN or MANY
instances; to improve performance of this operation, on the multi-valued side, create an index
on the relationship property. This also improves performance of the Execute, Fetch, and
Close methods. When defining a relationship property, Studio asks if you want such an index.
14.4.1 Referential Integrity
Relationships maintain referential integrity by enforcing constraints and invoking referential
actions. When a relationship is saved, Caché checks for the existence of the target of its reference.
If the target does not exist, then Caché returns an error and the save operation fails.
When an object is deleted and there are objects related to it, the related objects are deleted
(parent/child cardinality) or the delete operation fails (one/many cardinality).
14.4.2 Persistent Behavior of Dependent Relationships
With parent/child relationships, deleting the parent kills the children. Further, the storage of
children is subordinate to that of the parent, in a structure similar to the following:
^Inv(1)
^Inv(1, "invoice", 1)
^Inv(1, "invoice", 2)
^Inv(1, "invoice", 3)
...
Persistent Behavior of Relationships
Again, by associating the storage nodes of the CHILDREN with that of their PARENT, as
is depicted above, Caché can read and write more quickly.
Using Caché Objects 131