Rails - Feb 2009 - delete_if does not work on associations

I tried to user delete_if on an association:

class Group < ActiveRecord::Base
  has_many :memberships, :dependent => :destroy
  has_many :users, :through => :memberships

  ...
end

This is the controller method, trying to use delete_if. Although some
elements are removed (s2 < s1), the save method does not update the
association.

def intersect_or_remove_group
    other_group = Group.find(params[:group_id])
    s1 = @group.users.size
    case params[:submit]
      when "Intersect"
        @group.users.delete_if  { |u| !other_group.users.include?(u) }
      when "Remove"
        @group.users.delete_if { |u| other_group.users.include?(u) }
    end
    s2 = @group.users.size
    if s2 < s1
      @group.save
    end
    redirect_to @group
  end

If I rewrite it like this, it works just fine:

 def intersect_or_remove_group
    other_group = Group.find(params[:group_id])
    s1 = @group.users.size
    to_be_deleted = Array.new
    case params[:submit]
      when "Intersect"
        @group.users.each { |u| to_be_deleted << u if !
other_group.users.include?(u) }
      when "Remove"
        @group.users.each { |u| to_be_deleted << u if
other_group.users.include?(u) }
    end
    to_be_deleted.each { |u| @group.users.delete(u) }
    s2 = @group.users.size
    if s2 < s1
      @group.save
    end
    redirect_to @group
  end

Is this a bug or a feature?

Thanks for any help in advance

Regards

Alexander

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On Feb 4, 11:33 pm,
"mrlongleg1...-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org"
<mrlongleg1...-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
wrote:
> I tried to user delete_if on an association:
>
> class Group < ActiveRecord::Base
>   has_many :memberships, :dependent => :destroy
>   has_many :users, :through => :memberships
>
>   ...
> end
>
> This is the controller method, trying to use delete_if. Although some
> elements are removed (s2 < s1), the save method does not update the
> association.
Looks like delete_if just acts on the target array, not the
association itself (as a slight typing saver you can pass an array to
delete.

Fred
>
> def intersect_or_remove_group
>     other_group = Group.find(params[:group_id])
>     s1 = @group.users.size
>     case params[:submit]
>       when "Intersect"
>         @group.users.delete_if  { |u| !other_group.users.include?(u) }
>       when "Remove"
>         @group.users.delete_if { |u| other_group.users.include?(u) }
>     end
>     s2 = @group.users.size
>     if s2 < s1
>       @group.save
>     end
>     redirect_to @group
>   end
>
> If I rewrite it like this, it works just fine:
>
>  def intersect_or_remove_group
>     other_group = Group.find(params[:group_id])
>     s1 = @group.users.size
>     to_be_deleted = Array.new
>     case params[:submit]
>       when "Intersect"
>         @group.users.each { |u| to_be_deleted << u if !
> other_group.users.include?(u) }
>       when "Remove"
>         @group.users.each { |u| to_be_deleted << u if
> other_group.users.include?(u) }
>     end
>     to_be_deleted.each { |u| @group.users.delete(u) }
>     s2 = @group.users.size
>     if s2 < s1
>       @group.save
>     end
>     redirect_to @group
>   end
>
> Is this a bug or a feature?
>
> Thanks for any help in advance
>
> Regards
>
> Alexander
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Thanks for the hint.

Probably this is a bug, because the association is not updated
correctly. Unfortunately I am not advanced enough in rails to be able
to provide a patch for it.

Alexander alias MrLongleg

On 5 Feb., 04:38, Frederick Cheung
<frederick.che...-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
wrote:
> On Feb 4, 11:33 pm,
"mrlongleg1...-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org"
>
> <mrlongleg1...-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:
> > I tried to user delete_if on an association:
>
> > class Group < ActiveRecord::Base
> >   has_many :memberships, :dependent => :destroy
> >   has_many :users, :through => :memberships
>
> >   ...
> > end
>
> > This is the controller method, trying to use delete_if. Although some
> > elements are removed (s2 < s1), the save method does not update the
> > association.
>
> Looks like delete_if just acts on the target array, not the
> association itself (as a slight typing saver you can pass an array to
> delete.
>
> Fred
>
>
>
> > def intersect_or_remove_group
> >     other_group = Group.find(params[:group_id])
> >     s1 = @group.users.size
> >     case params[:submit]
> >       when "Intersect"
> >         @group.users.delete_if  { |u| !other_group.users.include?(u) }
> >       when "Remove"
> >         @group.users.delete_if { |u| other_group.users.include?(u) }
> >     end
> >     s2 = @group.users.size
> >     if s2 < s1
> >       @group.save
> >     end
> >     redirect_to @group
> >   end
>
> > If I rewrite it like this, it works just fine:
>
> >  def intersect_or_remove_group
> >     other_group = Group.find(params[:group_id])
> >     s1 = @group.users.size
> >     to_be_deleted = Array.new
> >     case params[:submit]
> >       when "Intersect"
> >         @group.users.each { |u| to_be_deleted << u if !
> > other_group.users.include?(u) }
> >       when "Remove"
> >         @group.users.each { |u| to_be_deleted << u if
> > other_group.users.include?(u) }
> >     end
> >     to_be_deleted.each { |u| @group.users.delete(u) }
> >     s2 = @group.users.size
> >     if s2 < s1
> >       @group.save
> >     end
> >     redirect_to @group
> >   end
>
> > Is this a bug or a feature?
>
> > Thanks for any help in advance
>
> > Regards
>
> > Alexander
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