Assignment expression rules automatically set values for one or more parameters using formulas called parameter expressions. The rule is controlled by a Boolean trigger expression. When this trigger expression evaluates to true, the rule's parameter expressions are executed in order from top to bottom.
Definition of trigger and actions
An assignment expression rule consists of a trigger and one or more actions.
The trigger expression is a Boolean formula, and the rule fires when this expression becomes true. By default, the rule triggers exactly once when the evaluation of the trigger expression switches from false to true. However, you can enable a setting to make the rule trigger continuously as long as its trigger expression remains true. An empty trigger expression is treated as always true.
The actions consist of one or more parameter expressions, which serve as formulas to set the value of parameters or multi-choice values. These parameter expressions are executed sequentially from the top to the bottom of the list.
Note: Other system rules are executed immediately after each parameter is set. However, the assignment expression rule itself will not be re-triggered for the same configuration until all its parameters have been fully evaluated.
Clearing parameter values
An assignment expression rule can also clear parameter values (setting them to null). This is done by adding a parameter to the action list without providing a formula for their assigments. For Boolean parameters and multi-choice values, indeterminate acts as the null value (meaning it is neither true nor false).
Behavior settings
Assignment expression rules include settings to control their behavior:
Setting name |
Description |
|---|---|
Trigger continuously |
The rule triggers every time the server executes rules as long as the trigger expression remains true, rather than only when it switches from false to true. Note: Assignment expression rules without Trigger continuously enabled will not trigger when opening a saved configuration. This is because they only fire when the evaluation result of the trigger expression actively switches from false to true during a live configuration session. |
Read also about site effectivity for rules.
