Using Caché Objects - InterSystems Documentation

Objects and SQL
The way to determine if a field is Always Computed or Triggered Computed is by the
TRANSIENT and/or CALCULATED property keywords. If the property is transient or calculated,
and has SQLCOMPUTED, the compute type is Always. If the property is not transient, not
calculated, and has SQLCOMPUTED, the compute type is Triggered.
An Example
Suppose a class has a Name property of the form last,first. You might use the value stored
in this property to create the calculated fields FirstName and LastName (each containing the
first and last name, respectively). To do this, the code to set the value of the computed
LastName field would be:
Set {LastName}=##class(MyClass).GetLastName({Name})
where MyClass is the class being projected and GetLastName is a class method which has
the following code in it:
Quit $Piece(Name,",")
This code simply returns the first element in the Name property that appears before the “,”
delimiter.
13.2.3 Methods
A class' instance methods are only accessible via the object representation of a class, and not
via SQL. This is because an SQL query does not cause objects to be instantiated their (hence,
their methods are not accessible).
13.2.4 SQL Triggers
Because Caché SQL supports the use of triggers, any trigger associated with a class is included
as part of the class' SQL projection.
For more information on triggers, see the section Triggers in Using Caché SQL.
Triggers are code segments executed when specific events occur in Caché SQL. Caché supports
triggers based on the execution of INSERT, UPDATE, and DELETE commands. The
specified code will be executed either immediately before or immediately after the relevant
command is executed, depending on the trigger definition. Each event can have multiple
triggers as long as they are assigned an execution order.
Triggers are not fired by the persistence methods used by the default storage class,
%CacheStorage.
122 Using Caché Objects