Allow multiple triggers on same event

[jcraigk]

Currently if multiple triggers are defined on :insert, for example, the second trigger overwrites the first one as the trigger naming in the auto-generated migration is based only on model and event. Adding an auto-incrementing integer at the end of the trigger name would allow for multiple triggers.

An example use case here is needing multiple pg_advisory_xact_locks on another table based on different fields in the triggering record. For example, a Message sent from from_user_id to to_user_id would need two separate locks on User to handle messages_received_count and messages_sent_count respectively. If there is another way to handle this or if multiple triggers on :insert is a bad idea, please comment.

[jcraigk]

Update: Using pg_advisory_unlock_all() and related functions (depending on your database) within a given set of SQL in a single trigger seems to work fine. This overcomes the need for multiple triggers for me but interested in others' opinions.

[wwahammy]

I was just caught by this in migrating to using hair_trigger with my Postgres database. Multiple triggers per-event would be amazing.

[jenseng]

You should be able to define multiple triggers using trigger groups ... e.g.

trigger.after(:update) do |t|
  t.all do # every row
    # some sql
  end
  t.of("foo") do
    # some more sql
  end
  t.where("OLD.bar != NEW.bar AND NEW.bar != 'lol'") do
    # some other sql
  end
end

Would that resolve your use case? One gotcha might be if you're doing this in a migration instead of a model, you may need to drop and recreate all the triggers for the group whenever you want to add a new one 🤔