Creating (Registering) Topics

The event_bus library emits all events with topic names. Topic name is simply an atom type variable. For example; if you want to emit an event after creating users, then :user_created could be a good name for the event topic. And before delivering this events for :user_created topic, you will need to register the topic name(:user_created) once in the app life cycle.

The event_bus library allows creating/registering topics in two ways:

• Using your project configuration file config.exs (recommended)
• Using register_topic/1 function (on demand)

Creating topics using your project configuration file

If you will use the same topic name on all environments, then config.exs would be a suitable place for registering your topic names. If you are planning to use a topic name only in production environment then you can choose to register on prod.exs file:

config :event_bus,
  topics: [
    :checkout_completed, 
    :email_sent,
    :payment_failed, 
    :user_created, 
    :user_activated,  
    # more topics...
  ]

Creating topics on demand using register_topic/1 function

On any part of application you can register topics using register_topic/1 function. Please note that the function only accepts atom() as input type:

EventBus.register_topic(:user_created)
EventBus.register_topic(:user_activated)
EventBus.register_topic(:email_sent)
...

Congratulations!!! With the registration of an event topic, event_bus library become ready to emit events. The next step is creating an event using the registered topics in the application.