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bcquality/microsoft/knowledge/events/add-new-event-parameters-at-the-end.md
Jesper Schulz-Wedde faeacb2484 Add 12 general AL event-design articles to events domain 
Add 12 atomic knowledge articles under microsoft/knowledge/events covering
general AL event-design best practices: IsHandled initialization and OnAfter
preservation, appending new event parameters, position-based event naming,
reusing/extending events, avoiding per-iteration publishing, Temp-prefixing
temporary record parameters, unabbreviated parameter names, preferring the
this keyword over IncludeSender, avoiding loosely typed parameters, not
mutating existing event contracts, and not bypassing critical operations
with IsHandled. Each article ships a .good.al and .bad.al demonstration
sample (object IDs 50240-50296; not compiled by CI). Extend the
al-events-review leaf Worklist with one targeted check per new rule.

Additive only; no contract or wiring change (events leaf already wired).

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
2026-06-25 11:58:59 +02:00

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bc-version domain keywords technologies countries application-area
all
events
event-parameters
signature
backward-compatibility
append
onbefore
integration-event
versioning
al
w1
all

Add new event parameters at the end

Description

Adding a parameter to an existing event publisher changes its signature, and every subscriber must be updated to match. Appending the new parameter at the end of the parameter list keeps the change easy to review and minimizes churn: existing subscribers still bind to the leading parameters, and the diff is a single clean addition. Inserting a parameter in the middle shifts every following argument, makes diffs noisy, and is error-prone to reconcile across many subscribers — a subscriber that compiles can still receive the wrong values because positions moved. New parameters belong after the existing ones.

Best Practice

When extending an existing publisher, append the new parameter after all existing ones, including after a trailing var IsHandled: Boolean when present. Subscribers that already match keep working against the leading parameters, and the change stays a one-line addition that is trivial to review.

See sample: add-new-event-parameters-at-the-end.good.al.

Anti Pattern

Inserting a new parameter in the middle of an existing event's signature, shifting the position of every subsequent argument and forcing a careful re-map of all subscribers. Detection: a changed event signature where an added parameter appears before existing parameters rather than at the tail of the list.

See sample: add-new-event-parameters-at-the-end.bad.al.