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* Add P0 extensibility compatibility knowledge Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com> Copilot-Session: 645349fd-1892-48f3-8a84-db77d6abd1c3 * Correct event compatibility guidance Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com> Copilot-Session: 645349fd-1892-48f3-8a84-db77d6abd1c3 --------- Co-authored-by: Jesper Schulz-Wedde <jesper.schulzwedde@microsoft.com>
26 lines
1.5 KiB
Markdown
26 lines
1.5 KiB
Markdown
---
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bc-version: [all]
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domain: events
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keywords: [event-parameters, signature, backward-compatibility, public-event, local-event, internal-event, appsourcecop, as0024, as0025]
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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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# Event parameter additions depend on publisher access, not position
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## Description
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Event subscribers bind publisher parameters by name and can omit parameters they do not use. A `local` or `internal` Business or Integration event can therefore gain a parameter at any position without breaking subscriber-only consumers; appending is not a compatibility requirement. A public event is also a public procedure that dependent extensions can raise, so adding a required parameter anywhere breaks callers under AppSourceCop AS0024.
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## Best Practice
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Add a parameter directly only when the shipped event publisher is `local` or `internal`. Place it where the signature is clearest; existing subscribers continue binding the parameters they name. For a public event, keep the original publisher unchanged and introduce a new event with the expanded contract.
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See sample: `add-new-event-parameters-at-the-end.good.al`.
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## Anti Pattern
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Appending a parameter to a public event and assuming its position makes the change compatible. Existing external callers still lack the new required argument. Conversely, do not flag a parameter inserted among existing parameters on a `local` or `internal` Business or Integration event merely because it was not appended.
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See sample: `add-new-event-parameters-at-the-end.bad.al`.
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