Removing events

[gtrias]

Hi,
We're started using you amazing library to publish and store several events but I just realized there are some of them which shall be removed. I'm trying to figure how I can create a migration to do it but I didn't find any destroy, remove or delete method which can help me doing that.

Is there a way to remove already persisted events?

[mpraglowski]

Hi
Why would you like to remove events? The events are the facts that has already happened - you shpuld not change the past.

Maybe some strategies for event versioning could help you. Please take a look at great book by Greg Young (avaiable for free to read online): https://leanpub.com/esversioning/read_full

[mpraglowski]

Is there a way to remove already persisted events?

There is no API for that on RES.

[gtrias]

Thank you for the book reference :)
We accidentally persisted some non wanted events and I want to just clean event store of such events... We're in a phase of experimentation with events right now.

[mostlyobvious]

Provided you're on ActiveRecord adapter, following can help you in phase of experimentation:

event = RailsEventStoreActiveRecord::Event.find(...)
RailsEventStoreActiveRecord::EventInStream.where(event_id: event.id).delete_all
event.destroy

[prasannatamma]

RailsEventStoreActiveRecord::Event not working

[mostlyobvious]

RailsEventStoreActiveRecord::Event has been marked as private along the way, not to become depended on. In a special case like unsupported deletes, one can define:

TemporaryEvent = Class.new(ActiveRecord::Base) { self.table_name = "event_store_events" }
TemporaryEventInStream = Class.new(ActiveRecord::Base) { self.table_name = "event_store_events_in_streams" }

[gtrias]

Thanks @pawelpacana I'm going to play with the ActiveRecord adapter right now. I'll share any success or failure here :)

[paneq]

RailsEventStoreActiveRecord::EventInStream.where(event_id: event.id).delete_all

this is dangerous for explicitly ordered streams (that use expected_version - https://railseventstore.org/docs/publish/#expected_version) for example those created by AggregateRoot. It should be ok, if that's not the case.

[gtrias]

Finally I've made a simple script running the queries directly against mysql.

module EventSystem
  module Tooling
    class EventDestroyer
      # @param event_ids [Array<String>]
      def initialize(
        event_ids:
      )
        @event_ids = event_ids
      end

      def call
        event_ids_str = @event_ids.to_s.tr('[]','')
        ActiveRecord::Base
          .connection
          .execute("DELETE FROM event_store_events WHERE id IN(#{event_ids_str})")

        ActiveRecord::Base
          .connection
          .execute("DELETE FROM event_store_events_in_streams WHERE event_id IN(#{event_ids_str})")
      end
    end
  end
end

Note that event_id field declared in event_store_events_in_streams table is not a FK to event_store_events so, If you only remove the events the RailsEventStore will break with errors of type:

NoMethodError:   undefined method `id' for nil:NilClass

[mpraglowski]

The script should work, however https://github.com/RailsEventStore/rails_event_store/blob/master/rails_event_store_active_record/lib/rails_event_store_active_record/generators/templates/create_event_store_events_template.rb#L9 - position values for stream in event_store_events_in_streams might be invalid. This might cause some issues later.

[gtrias]

Thanks for the reply @mpraglowski ,

We have the position field set at NULL in all events, it's only filled when you use the expected_version functionality?

[mpraglowski]

It is explained in https://railseventstore.org/docs/expected_version/

You probably do not use :auto strategy, and always keep the RES default :any.
That's why you do not have position value set. In your case it is 👍 :)