More about Declare OnChange rules
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Process Commander tracks properties listed in Declare OnChange rules for changed values. After each activity step, and after forward chaining for Declare Expression rules and constraints rules occurs, tracked changes start the activity specified on the OnChange Properties tab.
The activity identified on the OnChange
Properties tab must have an Activity Type of
OnChange. It can call or branch to other activities, but
only if they too have an Activity Type of
OnChange. DISPUTED Clinic 1/26/06
Your activity can examine the Value List property
pyChangedProperties to discover the property that changed
value. This property is on the page named
pyDeclarativeContext, of class
Code-Pega-DeclarativeContext. This page exists only while
the activity runs. STEWS
The primary page passed to OnChange activities is the top-level page.
OnChange processing may start as the result of a user HTTP Post operation. If users complete an HTTP form that changes the value of a property tracked by a Declare OnChange processing, this change is detected. SR-866 B-15857 B-16005
Use care not to start an infinite processing
loop within declarative rules. For example, in an OnChange activity, do
not update any of the properties that caused the activity to start. You
can to update other properties in the OnChange activity.
SR-3225
Declare Expression rules do not evaluate during
the execution of an OnChange activity. Clinic CLINB
1/26/05 However, do not attempt in an OnChange activity to overtly
set the value of a property that is the target of a Declare Expression
rule.
Similarly, constraints rules do not evaluate
during the execution of an OnChange activity. BUG-5313
During execution of a Declare OnChange rule, the page on which the
rule operates becomes the primary page. The page keyword
PRIMARY and the results of the
tools.getPrimaryPage() PublicAPI method reflect this change.
When the Declare OnChange rule execution completes, the primary page of
the calling activity resumes as primary. ERSNG 10/30/07
Design the OnChange activity to execute
quickly, as some properties may change values often. Remember that
properties may change values (and thus cause the rule to run) during
development and testing tasks, such as the preview of a harness or flow
action form. CLINB 10/13/05
Declare OnChange rules may be expensive
(computing several values) compared with Declare Trigger rules that test
the same property. Consider which rule type better meets your needs. For
example, if a value changes every few seconds but is part of an object
that is saved only hourly on average, a Declare Trigger rule computes a
new value only hourly, not in real time.
C-446 Using the Tracer, you can watch the evaluation of a
Declare OnChange rule. Start the Tracer and select a requestor session.
Click the Options button(
) and check the Declare
OnChange box in the Event Types to Trace
section. Also check the RuleSet that contains the rule to be traced.
The statistic Tracked Property Changes on the full
details page of the Performance tool shows how many property changes have
occurred (for the current requestor since log-in) that are tracked for
declarative rules computations. You can modify the
prlogging.xml file to log additional details about tracked
property changes. See Pega Developer Network article 
PRKB-18112 How to identify which properties are tracked for
declarative processing.
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declaration, forward chaining |
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Debugging with the Tracer |