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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
1.7 KiB
Markdown
26 lines
1.7 KiB
Markdown
---
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bc-version: [all]
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domain: performance
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keywords: [event-subscriber, guard, db-call, frequently-fired, validate]
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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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# Guard event subscribers with cheap checks before any database call
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## Description
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Event subscribers fire on every event matching their signature — for `OnAfterValidateEvent` on a hot field like `Sales Line.Quantity`, that is every quantity edit by every user. Per the upstream guidance, "Keep event subscriber code lightweight" and "Avoid database operations in frequently-fired events — guard with cheap checks first." A `Get` or `FindFirst` at the top of such a subscriber pays a database round-trip on every fire, including the calls for which the subscriber's work was not needed.
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## Best Practice
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Open the subscriber with an in-memory predicate that filters out the calls the subscriber does not handle — record type, document type, status, parameter-passed flags. Only after the cheap guard passes should the body issue a database call, and only with `SetLoadFields` for the columns the body actually reads.
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See sample: [`guard-event-subscribers-before-db-call.good.al`](guard-event-subscribers-before-db-call.good.al).
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## Anti Pattern
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`[EventSubscriber(...'OnAfterValidateEvent', 'Quantity', ...)] local procedure ... var Item: Record Item; begin Item.Get(Rec."No."); if Item.HasCustomPricing() then ...;` — `Item.Get` runs on every quantity change, including changes to lines whose `Type` is not `Item`. A pre-check `if Rec.Type <> Rec.Type::Item then exit;` ahead of the `Get` removes most of the calls.
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See sample: [`guard-event-subscribers-before-db-call.bad.al`](guard-event-subscribers-before-db-call.bad.al).
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