- add :user_id, references(:users, on_delete: :delete_all)
- add :activity_id, references(:activities, on_delete: :delete_all)
- add :seen, :boolean, default: false
+ add(:user_id, references(:users, on_delete: :delete_all))
+ add(:activity_id, references(:activities, on_delete: :delete_all))
+ add(:seen, :boolean, default: false)