Consumers

[vladfaust]

Introduce consumers which are guaranteed to handle an event exactly one time, based on their name (or class name if it is a class):

struct UserCreated
  include Onyx::EDA::Event

  def initialize(@user_id : Int32, @registration_request_id : String)
  end
end

struct RegistrationRequest
  include Onyx::EDA::Event

  def initialize(@name : String)
  end
end

# ---

class Registrar
  include Onyx::EDA::Consumer(RegistrationRequest)

  def consume(event)
    user = Onyx.query(User.new(name: event.name).insert.returning(:id))
    Onyx.emit(UserCreated.new(user.id, event._event_id))
  end
end

spawn Registrar.new.listen # RFC on better name

# Or

Onyx.consume(RegistrationRequest, name: "registrar") do |event|
  user = Onyx.query(User.new(name: event.name).insert.returning(:id))
  Onyx.emit(UserCreated.new(user.id, registration_request_id: event._event_id))
end

# ---

event_id = Onyx.emit(RegistrationRequest.new("John"))

Onyx.subscribe(self, UserCreated, event_id) do |event|
  pp event.user_id
end

An event can be broadcast to an arbitrary amount subscribers, but only to one consumer of this name. However, there can be an arbitrary amount of consumers with different names, for example in addition to the example above:

class AdminNotifier
  include Onyx::EDA::Consumer(RegistrationRequest)

  def consume(event)
    send_admin_email("New registration request")
  end
end

[aemadrid]

that interface looks great. I'm guessing you will use redis streams and consumer groups?

[vladfaust]

@aemadrid for Redis, yes. BTW, I'm also planning on adding different MQs.