Events were introduced in Dynamics NAV 2016.

But you’re asking — what are events?

In short, Events in Dynamics NAV/Business Central implement a Design Pattern known as the “Observer Pattern.”

Explanation

In Dynamics NAV/Business Central, you can create new functions and make them Events. An Event can be of type Subscriber or Publisher.

Publisher Event Types:

  • Integration
  • Business

(You may also see Global and Trigger types, but you can only define the first two)

The difference?

  • Business Events: Microsoft guarantees they won’t be removed in future versions.
  • Integration Events: These might be removed if deemed not useful by Microsoft.

What’s the Difference Between a Publisher and a Subscriber?

  • A Publisher knows its Subscribers.
  • A Publisher stays alert to a certain condition and, when met, it calls the subscriber to act.

Think of the Subscriber as the response to a given situation monitored by the Publisher.

  • One Publisher can have many Subscribers.
  • One Subscriber can only have one Publisher.

Built-in Events in NAV/Business Central

All table and page triggers like:

  • Insert
  • Modify
  • Delete
  • Validate

...have two default publishers:

  • OnBeforeInsertEvent
  • OnAfterInsertEvent

Note:

Since a Publisher can have multiple Subscribers, execution order is not guaranteed.

So, if you want sub1 to run before sub2, you need to:

  • Remove sub2
  • Combine its logic inside sub1

Practical Example

You might start with:

// Sub1 and Sub2 both subscribing to the same event
[EventSubscriber(...)]
procedure Sub1(...)

[EventSubscriber(...)]
procedure Sub2(...)

After applying the workaround:

// Only Sub1 remains, containing logic from both
[EventSubscriber(...)]
procedure Sub1(...)
    // Logic for Sub1
    // Logic for Sub2

The Observer Pattern

Let’s compare it to the Observer Pattern:

Class Diagram Focus:

class diagram

Subject:

  • Holds a list of Observers (observerCollection)

  • Functions:

    • registerObserver → Adds an observer
    • unregisterObserver → Removes an observer
    • notifyObservers → Invokes all observers

Observer:

  • Has one method: update (the response to the subject)

Sequence Diagram

sequence diagram

  1. Subject s1 adds Observer o1 and Observer o2 (attach/register).
  2. The monitored condition occurs (notifyObservers).
  3. Observer o1 is invoked.
  4. Then Observer o2.

Mapping to NAV/BC

Observer Pattern Dynamics NAV/BC
Subject Publisher
Observer Subscriber

TIP

You can check subscribers in NAV/Business Central via the Event Subscriptions page.

Example link (BC14 Web Client):

http://bc14/NAV/?company=CRONUS%20International%20Ltd.&page=9510