Object relations in memory

Hi all!

I have the following situation:

I'm creating an application where I have groups that can contain groups.
I do in the following way:

class Group < ActiveRecord::Base
  belongs_to :group, :class_name => 'Group', :foreign_key => 'group_id'
  has_many :groups, :class_name => 'Group', :foreign_key => 'group_id'
end

This works very well. I can do group.groups and group.group stuff.

The problem with this situation is that it's possible to create cycles:

Group A belongs_to --> Group B belongs_to --> Group C belongs_to -->
Group A

Now, I created a method of checking for cycles and added this to my
Group model, so I can ask if specific model object creates a cycle. So
far so good..

Since I don't want to have cycles in my application, I want to check for
cycles before I save the model, so I want to use my check method as a
validator. The problem I'm facing is that when I create a model, the
whole relational model of objects isn't reflected in memory.

The following happens (let's say I want to update a model). I create 3
groups that form a cycle as above and save them to the database. Now I
load group C and do a c.group = nil. This should break the cycle, but
when calling c.cycle?, I still get that C causes a cycle. On inspection
of group A, I get that A.groups still includes group C.

Since I want to use the check for validation, I don't want to save to
the database before I'm sure that there are no cycles.

Is there a way to overcome this?