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bcquality/microsoft/knowledge/events/add-new-event-parameters-at-the-end.md
Jesper Schulz-Wedde 0ad92cad86 Refine events articles after review feedback 
Correct wording in five events articles to reflect that AL event
subscribers bind by parameter name, not position:

- add-new-event-parameters-at-the-end: drop the inaccurate claim that
  appending a parameter forces subscribers to be updated or causes wrong
  values; keep the append-at-end best practice.
- do-not-add-ishandled-to-an-existing-event: reframe from "breaking
  change" to the semantic/purpose shift that leaves existing subscribers
  pointless; rename the breaking-change keyword to semantic-change.
- name-events-by-publisher-position: extend the good sample with
  position-named publishers raised from table and report trigger
  contexts.
- initialize-ishandled-to-false-before-publishing: scope the detection
  and best practice to events that actually carry a var IsHandled, so an
  OnBefore with no IsHandled is not flagged.
- do-not-bypass-critical-operations-with-ishandled: add a litmus-test
  definition of a critical operation (code that cannot stand as an
  independent, self-contained unit).

Knowledge-only; no contract or wiring change.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
2026-06-25 11:59:00 +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. Appending the new parameter at the end of the parameter list keeps the change easy to review and track: existing subscribers still bind to the leading parameters, and the diff is a single clean addition. Inserting a parameter in the middle makes diffs noisy and harder to review, and obscures the history of how the signature evolved. 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.