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Support Article

Error thrown on UI when looping Through embeded page



Post upgrade to Pega Platform 8.3.1, error occurs on the Activity Rule form when looping through an embedded page.

Error Messages

Step page—Invalid expression or reference: When used with a "For Each Embedded Page" option, the Step page should reference a list or group property.

Steps to Reproduce

  1. Upgrade PRPC 6.1 SP2 to Pega Platform 8.3.1.
  2. Loop through an embedded page.
  3. Specify a PageList property on a StepPage.
  4. Click Save. Error occurs on the Activity rule form.

Root Cause

This behavior is as per Pega product design.
The error occurred due enhanced validations in higher Pega versions compared to PRPC 6.x.


Here's the explanation for the reported behavior:
  1. When a PageList is specified as a StepPage in a Looping activity, the rules cannot be saved because only one entry is provided in the Pages & Classes for a Looping StepPage.
    For example,

    When the StepPage expression is A.B.PageList, two entries must be present in the Pages & Classes. One entry for A (such that each property is resolved down the chain till the PageList) and another for A.B.PageList (which defines the Class of each Page in the Page List).

  2. Pages & Classes must be modified to resave the rule. When the problem rules are originally saved in PRPC 6.x, the validation to save is less strict than it is in Pega Platform 8.

    In Pega Platform 8, the user must guarantee that a PageList exists at the time of assembly instead of encountering a runtime error for a non-existent PageList.
To correct these rules, define an entry for the Top level property in the PageList expression (as in Point 1). 
Additionally, remove all ambiguous references. As part of the tightening of Pega Platform 8 Validations, the system displays errors wherever there is ambiguity.

Published June 9, 2020 - Updated December 2, 2021

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