Declare Expression rules
Completing the New or Save As form

Field

Description

Select Declare Expression from the Decision category.

Select an internal or external class for this rule. The properties to be calculated can be in this class or in the class of an embedded page.

If you select a class derived from the Embed- base class, leave the Page Context key part blank, and create a context-free expression.

You cannot use a Rule-Declare-* class or any ancestor of the Rule-Declare- class (including @baseclass) here. You cannot use a class derived from the Code- class here.

You can't create rules with Work- as the Applies To class. Instead, choose a class derived from Work-, such as a work type or work pool container class. In many cases, the Save As dialog box defaults a container class for this field. See Copying standard rules from the Work- class.

Identify a property that appears somewhere within the object of the class in the Applies To key part. Precede the name with a period. Select a property of mode Single Value, Page, or Java Property.

You can't use a Declare Expression rule to compute a property for which the Cannot be declarative target box (on the Advanced tab) is selected.

You can't use symbolic page names such as primary or steppage here, because they are meaningful only in an activity execution context.

Optional. Leave this blank if the Target Property property has mode Single Value and appears directly on a page of the Applies To class, or if creating a context-free expression.

Otherwise, identify a Page List or Page Group property reference plus parentheses. Omit any index between parentheses, as the expression applies to all elements. For example, these show correct use:

Invoices.pyOrders().pyItems().pyItemNames()
pyWork.pxCorrSummary()

The length of the value in this field is limited to 64 characters.

Forward chaining does not create embedded pages where none existed before. Declare Expressions that have a non-blank Page Context and that use top or parent keywords do not execute unless there is at least one pre-existing embedded page at each level of the page context. For more information and an example, see Pega Developer Network article PRKB-21038 Declare expression rules using the TOP or PARENT keyword depend on existing pages to run.