AL Events¶


File	`al-events.instructions.md`
Applies to	`*/.al`
Activation	Context-activated (event code)
Role	Event-driven patterns

Purpose¶

Event-driven architecture patterns for extensible Business Central applications. Covers EventSubscribers, IntegrationEvents, BusinessEvents, and the publisher/subscriber model.

Key rules¶

Rule	What it enforces
EventSubscriber	Subscribe to BC events (`OnBeforeInsert`, `OnAfterModify`, etc.)
Handler suffix	Subscriber codeunits end with `Handler`
IntegrationEvent	Create extensibility points in your own code
Handled pattern	Use `IsHandled: Boolean` parameter for overridable logic
No direct modification	Never modify base objects — always use events

Pattern: EventSubscriber¶

codeunit 50100 "Sales Document Events Handler"
{
  [EventSubscriber(ObjectType::Table,
    Database::"Sales Header",
    OnBeforeInsert, '', false, false)]
  local procedure OnBeforeInsertSalesHeader(
    var SalesHeader: Record "Sales Header";
    RunTrigger: Boolean)
  begin
    ValidateCustomFields(SalesHeader);
  end;
}

Pattern: IntegrationEvent with Handled¶

procedure CreateCustomer(
  var Customer: Record Customer): Boolean
var
  IsHandled: Boolean;
begin
  OnBeforeCreateCustomer(Customer, IsHandled);
  if IsHandled then
    exit(true);
  Customer.Insert(true);
  OnAfterCreateCustomer(Customer);
  exit(true);
end;

[IntegrationEvent(false, false)]
procedure OnBeforeCreateCustomer(
  var Customer: Record Customer;
  var IsHandled: Boolean)
begin
end;

Source: instructions/al-events.instructions.md