I’ve written a lot in the past about handling breaking schema changes on extensions and the best practice to use the ObsoleteState object property to signal to your developers or third-party ISV users of your extensions that you’re planning to remove something in your codebase. You can find articles here and here.
Today I want to write a quick post for talking about events and about a worst practice that I see someone is doing on their extensions. As you know, events are a foundamental key concept in the extension’s world. If you have extension A that defines some business logic and then you have extension B (that depends on A), from B you can interact with the business logic defined on A only by subscribing to events raised by extension A:
When you create an extension with AL language, you can define two types of events:
The underlined text is extremely important in my opinion. If you declare that an event is a business event, you should not change it’s signature from version X to version X+1 of your extension. This is an error. Business events should be always documented together with the solution and if you’re an ISV you should provide their definition to your third-party users.
And what about if an event defined on version X will be never used in the future? You should never remove the event and release a version X+1 without this event. Instead, you should Obsolete the event on version X+1 and then gives the time to your extension’s users to react and adapt their code (yes, you can obsolete also events!).
As an example, imagine to have extension A that defines a business process in a codeunit. In this codeunit, you raise events for handling extensibility of your business process:
In extension B (that depends on A) you can attach to events raised by A by using event subscribers:
If you release version X+1 of your extension A and in this new version you decide to remove BusinessEvent1 (because it will be never used anymore), you can break other extensions:
What’s the best way to do this (if you really need to do this). On version X+1 of your extension A you can obsolete the BusinessEvent1 event as follows:
In this way your third-party users (other ISV and so on) will receive a warning on their code and they can act as needed:
Please remember this and use Obsolete property also on events if needed. This will guarantee you a more safe world