Rails core - Nov 2010 - Surprise in (delete_all | clear | destroy_all) on association

Hi,
 I was very surprised by difference of delete_all on association vs
model(delegated to relation).
Given TaskFilter.has_many(:qualifiers,
:class_name=>''TaskFilterQualifier'')

TaskFilter.delete_all => one DELETE statement

Without :dependent option on "qualifiers" association
TaskFilter.first.qualifiers.delete_all =>
  SELECT `task_filter_qualifiers`.* FROM `task_filter_qualifiers` WHERE
(`task_filter_qualifiers`.task_filter_id = 1)
  BEGIN
    UPDATE `task_filter_qualifiers` SET `task_filter_id` = NULL WHERE
`task_filter_qualifiers`.`task_filter_id` = 1 AND
`task_filter_qualifiers`.`id` IN (90, 91)
  COMMIT

Why UPDATE, not DELETE ?

With :dependent => :destroy
TaskFilter.first.qualifiers.delete_all =>

  TaskFilter Load (0.9ms)  SELECT `task_filters`.* FROM `task_filters` LIMIT
1
  TaskFilterQualifier Load (0.9ms)  SELECT `task_filter_qualifiers`.* FROM
`task_filter_qualifiers` WHERE (`task_filter_qualifiers`.task_filter_id = 1)
  SQL (0.2ms)  BEGIN
  AREL (6.6ms)  DELETE FROM `task_filter_qualifiers` WHERE
(`task_filter_qualifiers`.`id` = 92)
  TaskFilter Load (6.4ms)  SELECT `task_filters`.* FROM `task_filters` WHERE
(`task_filters`.`id` = 1) LIMIT 1
  AREL (0.6ms)  UPDATE `task_filters` SET `updated_at` = ''2010-11-24
09:28:03'' WHERE (`task_filters`.`id` = 1)
  AREL (2.6ms)  DELETE FROM `task_filter_qualifiers` WHERE
(`task_filter_qualifiers`.`id` = 93)
  TaskFilter Load (8.2ms)  SELECT `task_filters`.* FROM `task_filters` WHERE
(`task_filters`.`id` = 1) LIMIT 1
  AREL (1.7ms)  UPDATE `task_filters` SET `updated_at` = ''2010-11-24
09:28:03'' WHERE (`task_filters`.`id` = 1)
  SQL (53.5ms)  COMMIT

Note that I have :touch option, so sql below is produced by :touch callback
TaskFilter Load (6.4ms)  SELECT `task_filters`.* FROM `task_filters` WHERE
(`task_filters`.`id` = 1) LIMIT 1
  AREL (0.6ms)  UPDATE `task_filters` SET `updated_at` = ''2010-11-24
09:28:03'' WHERE (`task_filters`.`id` = 1)

That is nightmare, I expect delete_all to be fast sql query, but instead I
have:
* all associated objects loaded
* each object was destroyed, with many callbacks and DELETE queries

delete_all, clear, destroy_all respect :dependent option, but why ?
If association hasn''t :dependent option, then delete_all is duplicate
of
clear
if association has :dependent=> :destroy option, then delete_all, clear are
duplicates of destroy_all

delete_all work fine on relation so,
TaskFilter.first.qualifiers.scoped.delete_all will work fine:
  TaskFilter Load (1.3ms)  SELECT `task_filters`.* FROM `task_filters` LIMIT
1
  AREL (71.7ms)  DELETE FROM `task_filter_qualifiers` WHERE
(`task_filter_qualifiers`.task_filter_id = 1)

Is this all intentional behavior ?

Maybe this ticket is related
https://rails.lighthouseapp.com/projects/8994/tickets/5196-delete_allnullify-in-associations-does-uneeded-queries

Thanks,
Anatoliy Lysenko

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