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* Add events knowledge domain and review leaf skill Add a new `events` knowledge domain covering AL events & subscribers, wired into the AL review pipeline. - 3 atomic articles (+ .good.al/.bad.al samples) under microsoft/knowledge/events/: the IsHandled override pattern, thin OnBefore/OnAfter integration-event publishers, and static vs manual subscribers. - New leaf skill microsoft/skills/review/al-events-review.md sourcing the events domain. - Wired into microsoft/skills/review/al-code-review.md (sub-skills + Source + description) and README.md (leaf-skill count + domain list). AL event syntax verified against Microsoft Learn. Samples are demonstration-only (not compiled by CI). Additive change; no contract change. Part of #34. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com> * 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> * 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> * Soften Anti Pattern wording in add-new-event-parameters article Remove the last name-vs-position misconception from the Anti Pattern so it is consistent with the corrected Description: mid-list insertion is framed as noisy and harder to review rather than as forcing subscriber re-mapping. Detection sentence unchanged. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com> * Add events domain reviewers to CODEOWNERS Add @AleksandricMarko and @pchriste-microsoft-com as required reviewers for the events knowledge domain, matching the existing per-domain expert ownership convention. Inserted in alphabetical order ahead of the performance line. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com> --------- Co-authored-by: Jesper Schulz-Wedde <jesper.schulzwedde@microsoft.com> Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
26 lines
2.3 KiB
Markdown
26 lines
2.3 KiB
Markdown
---
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bc-version: [all]
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domain: events
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keywords: [ishandled, overridable, onbefore, integration-event, extensibility, event-override, subscriber-hook]
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technologies: [al]
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countries: [w1]
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application-area: [all]
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---
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# Use the IsHandled pattern to make base behaviour overridable
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## Description
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AL has no method overriding, so a `procedure` that runs its body unconditionally cannot be replaced by an extension without editing base code. The established Business Central seam for substituting default behaviour is the `IsHandled` pattern: the routine raises an `OnBefore…` integration event carrying a `var IsHandled: Boolean`, then exits early when a subscriber has set it. This hands a partner a sanctioned hook to replace the logic instead of overwriting the routine. LLMs trained on languages with inheritance emit routines whose logic always runs and expose no `OnBefore`/`IsHandled` seam, so the behaviour silently cannot be overridden.
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## Best Practice
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Raise `OnBeforeX(…, IsHandled)` as the first step of the routine and guard with `if IsHandled then exit;` before any default logic runs. Declare the publisher `[IntegrationEvent(false, false)] local procedure OnBeforeX(…; var IsHandled: Boolean)` with an empty body, and keep `IsHandled` a `var` parameter so a subscriber can write to it. A subscriber that replaces the behaviour does its work and sets `IsHandled := true`; one that only augments leaves it untouched and guards with `if IsHandled then exit;` itself. Reserve the override hook for cases where a partner genuinely needs to replace logic — when the goal is only to react, a positive `OnAfter` event is the better seam.
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See sample: `use-ishandled-to-make-base-behaviour-overridable.good.al`.
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## Anti Pattern
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Two shapes. First, a routine whose default logic always runs because there is no `OnBefore…`/`IsHandled` hook at all — extensions cannot change it without overwriting base code. Second, a routine that raises `OnBeforeX(IsHandled)` but omits the `if IsHandled then exit;` guard, so the default logic still executes after a subscriber set `IsHandled := true`, duplicating work and side effects. Detection: an `OnBefore` publisher with a `var IsHandled: Boolean` parameter whose caller never tests `IsHandled`, or a public routine doing non-trivial work with no overridable seam.
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See sample: `use-ishandled-to-make-base-behaviour-overridable.bad.al`.
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