add _delete key for accepts_nested_attributes_for ?

I wouldn't be sure there's the need for two different attributes. The behavior of the nested model depends of the relation configuration.
Here, you don't want the tag to be deleted when it's relation with the post is.

Then you set your relation with a :dependent option to delete.

has_many :tags, :through => :post_tags, :dependent => :delete

I guess every time you want to delete a nested relation, you want to do it the same way.
Or at least if at some point, you want to delete the tag, it's not an interface implementation but a logic one. So it should remain in the activerecord's relation.

I tried this way (and many other ways) of using :dependent, I think it doesn't work (I'm using rails on github). And in rails code it says:

#   *Warning:* This option is ignored when used with <tt>:through</tt> option.

ref: http://github.com/rails/rails/blob/master/activerecord/lib/active_r...

If this does work, then yes my proposal is needless.

louis vuitton watches

This request seems to have sense to me, since I agree with you there is no simple way (i.e. without using before_save hooks) to just delete the relationship without destroying the object. I would like to have the ticket re-opened or to see some more explanation.

P.S. the same is true if you have an HABTM relation instead of an has_many :through.

alberto

This request seems to have sense to me, since I agree with you there is no simple way

This request does not make any sense to me.
it does what it says, it destroys the tag.

the so call "no simple way"

 some_post.tags.clear

you may want to simply stick to associations instead of nested attributes for your use case.
or simply use has_and_belongs_to_many if your join model needs no logic.

Jan Xie

In this case, most people want to unlink post with tags only, instead of destroying tags (I guess).

if you want this you may simply want to use the shown method.
Also you probably want to define dependent destroy for the join model, so you dont leave orphans behind if you destroy a tag or a post.

class Post
  has_many :post_tags, :dependent => :destroy
end

class Tag
  has_many :post_tags, :dependent => :destroy
end

please set this to invalid.

I agree with almost everything. The only arguable thing is:

you may want to simply stick to associations instead of nested attributes for your use case.

If this is the philosophy behind nested attributes (i.e. «you simply CAN'T do this with nested attributes, manage the associations by your self, you moron!») than it's ok. But I don't see any reason why one shouldn't want this non-destructive behavior while still using nested attributes.

Btw, my "no simple way" referred to the fact that standard forms (e.g. nested_form_for) rely on the product.tags_attributes array. If you want to use them (and they're great to keep your views clean) and NOT destroy associated objects, you have to do something like

before_safe god_save_the_tags!
private
  def god_save_the_tags!
    tags.select(&:marked_for_detruction?).each do |tag|
      tag.reload # Notice that there is no "unmark_for_destruction" right now,
                 # but I'm pretty sure I saw a related ticket somewhere here
      tags.delete(tag)
    end
  end

I see.

It would be nive if :destroy and :delete would behave exactly as calling the corresponding methods on the association.