Rails - Nov 2006 - @article.article_groups.delete_if... Dosn''t work!

If I try:

      @article.article_groups.delete_if {|x|
        x.group_id == x.group_id
      }

It does nothing.

If I try:

      articletmp.article_groups.each{ |x|
              @article.article_groups.delete(y)
}

It deletes some of the groups.

@article.article_groups.clear
works.

Why dosn''t the to first examples work as expected??

Do I have to put groups I don''t want to be deleted inn as hidden
fields in my form? (I of course dosn''t want every groups to be deleted
as in the example above).

- Henrik