Should the changes be available in after-update?

[camsaul]

Use case: to log all the changes that were made to rows in the application database.

If there were some way to make the changes made available, or at least the ones made by Toucan -- probably ok to ignore ones done by DB triggers like ON UPDATE SET updated_at = now(), that could be useful. Could these be made available by a &changes anaphor in the after-update method? Or should after-update just see an instance with the t2/changes? Need to think about this.

[tsmacdonald]

This would be helpful to me. I have logic that I want to fire when a particular column has changed. If I do it in before-update, there's always a chance that the save could fail, so I want to do it in after-update.

I don't have strong feelings about whether I get them via t2/changes or &changes. t2/changes doesn't really make sense since the record would have already changed and I suppose there's a perverse case where there are additional changes that have happened since the update. But it would still be useful.

[camsaul]

So this does seem to work sometimes (as proven by #171) but in other situations it doesn't... in Metabase for example something with the :model/User model prevents it from working correctly

(toucan2.core/define-after-update :model/User
  [user]
  (println "ORIGINAL =>" (select-keys (toucan2.core/original user) [:is_superuser]))
  (println "NEW =>"      (select-keys user [:is_superuser]))
  (println "CHANGES =>"  (select-keys (toucan2.core/changes user) [:is_superuser]))
  user)

(defn x []
  (let [user         (toucan2.core/select-one :model/User)
        _            (println "USER =>" (select-keys user [:is_superuser]))
        updates      {:is_superuser (not (:is_superuser user))}
        _            (println "UPDATES =>" updates)
        rows-updated (toucan2.core/update! :model/User (:id user) updates)]
    (printf "Updated %d rows.\n" rows-updated)))

(x)
USER => {:is_superuser true}
UPDATES => {:is_superuser false}
ORIGINAL => {:is_superuser false}
NEW => {:is_superuser false}
CHANGES => {}
Updated 1 rows.

vs. a new model, which works correctly

(methodical.core/defmethod toucan2.core/table-name ::FakeUser
  [_model]
  "core_user")

(toucan2.core/define-after-update ::FakeUser
  [user]
  (println "ORIGINAL =>" (select-keys (toucan2.core/original user) [:is_superuser]))
  (println "NEW =>"      (select-keys user [:is_superuser]))
  (println "CHANGES =>"  (select-keys (toucan2.core/changes user) [:is_superuser]))
  user)

(defn x []
  (let [user         (toucan2.core/select-one ::FakeUser)
        _            (println "USER =>" (select-keys user [:is_superuser]))
        updates      {:is_superuser (not (:is_superuser user))}
        _            (println "UPDATES =>" updates)
        rows-updated (toucan2.core/update! ::FakeUser (:id user) updates)]
    (printf "Updated %d rows.\n" rows-updated)))

(x)
USER => {:is_superuser false}
UPDATES => {:is_superuser true}
ORIGINAL => {}
NEW => {:is_superuser true}
CHANGES => {:is_superuser true}
Updated 1 rows.

Not sure why :model/User doesn't work, maybe after-select or something is inadvertently discarding the changes... either way I think after-update should probably reset changes before calling the method to ensure the method sees the correct value

[tsmacdonald]

Seems like an underlying issue is that ORIGINAL is wrong: in your example it should be true and not false. I thought for sure it was something weird in before-update, but in a fresh REPL with no before-update I get the same behavior. Will look into this more tomorrow