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2b5550c346
Lead with a complete plugin quick start and add task-oriented usage, troubleshooting, customization, and contribution guides. Preserve the broader plugin framing, correct conflicting contract guidance, support Agents folder reviews, and align repository validation. Convert existing sample references to clickable links without changing knowledge rules. Co-authored-by: Jesper Schulz-Wedde <jesper.schulzwedde@microsoft.com> Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>
26 lines
1.8 KiB
Markdown
26 lines
1.8 KiB
Markdown
---
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bc-version: [all]
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domain: events
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keywords: [ishandled, semantic-change, event-contract, backward-compatibility, onbefore, integration-event, subscribers]
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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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# Do not add IsHandled to an existing event
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## Description
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Adding a `var IsHandled: Boolean` parameter to an event that already shipped without one silently changes the event's purpose — from a plain notification into an overridable seam. Existing subscribers were written against a "notify" contract they never agreed to make skippable, so their behaviour can quietly become wrong or pointless. The safe move is to leave the existing event untouched and introduce a new `OnBefore…` event carrying `IsHandled` at the point you want to make overridable. Existing subscribers keep working against the original event; new subscribers opt into the override seam through the new one.
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## Best Practice
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Keep the existing event as-is and add a separate `OnBeforeX(…; var IsHandled: Boolean)` before the logic you want to make overridable. Two events with distinct, stable contracts are safer than one event whose meaning and signature were changed under its subscribers.
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See sample: [`do-not-add-ishandled-to-an-existing-event.good.al`](do-not-add-ishandled-to-an-existing-event.good.al).
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## Anti Pattern
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Mutating a shipped event — for example adding `var IsHandled` to `OnAfterCalculateTotal` — to retrofit override behaviour, which overloads the event's meaning and undermines existing subscribers. Detection: an `IsHandled` parameter added to a pre-existing event signature rather than introduced through a new dedicated `OnBefore` publisher.
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See sample: [`do-not-add-ishandled-to-an-existing-event.bad.al`](do-not-add-ishandled-to-an-existing-event.bad.al).
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