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Contributed by CURABIS ApS, generalized from patterns observed across real AppSource/PTE development. Each article follows the knowledge file format (frontmatter, Description/Best Practice/Anti Pattern, sibling .good.al/.bad.al samples).
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Recalculate Stored Derived Fields Before Exposing Them on API Pages
Contributions welcome — open a PR to refine or extend this article.
Description
A stored field whose value is derived from other fields inside an OnValidate trigger only updates when that specific trigger fires. If the underlying source data changes through some other path, the stored value goes stale without raising any error. Exposing such a field directly on an API page hands external consumers a snapshot that may be significantly out of date.
Best Practice
Recalculate the derived value in OnAfterGetRecord from its authoritative source — typically a FlowField — using a page-level variable, and expose both the recalculated value and the source field so the consumer can verify it.
See sample: stored-derived-fields-must-not-be-exposed-directly.good.al.
Anti Pattern
Exposing the stored field directly via Rec, trusting that it was kept in sync by whichever trigger last touched it.
See sample: stored-derived-fields-must-not-be-exposed-directly.bad.al.