Managing acts_as_tree Model

I have a membership list based on the above. However, I allow for
prospective members to sign up with the reference (id) of a referer
(parent). So I am getting an id from ActiveView that I need to
validate and then slot the new member in as a child to the referer. I
managed to get the validation done to check that a member with the
supplied id does indeed exist, by adding the following to
validations.rb :

module ActiveRecord module Validations module ClassMethods def validates_id_exists(*attr_names) configuration = { :message => "is not valid" } configuration.update(attr_names.pop) if attr_names.last.is_a?(Hash)
    validates_each(attr_names, configuration) do |record, attr_name, 

record.errors.add(attr_name, configuration[:message]) unless
Member.find(:first, :conditions => [“id = ?”, value.to_i])

Note the find, using find(id) would have raised an exception that I
don’t want to deal with here. Then, in the model I just have:

validates_id_exists :associate_reference

Now for my question: I cannot really do the textbook
parent.children.create(), since I need to allow
Rails to do its magic with validation of all the other fields on the
form (email, psw etc). So I opted for the following (attaching the
umbilical cord AFTER the save of the new record):

attr_accessor :associate_reference def after_save if self.parent.nil? or self.associate_reference.to_i != # if new parent not same as old self.parent.children.delete(self) unless self.parent.nil? # remove me from old parent family parent = Member.find(self.associate_reference.to_i) # find new parent parent.children.push(self) # add me to new parent family # should be ok to do this here end end

It works, but I have a feeling there must be a more elegant way of
doing this. Any words from the wise?