passing values trough models.

So if I understand you correctly, it sounds like you have two models:
A and B. Model A has an attribute that allows text to be stored in it,
and this attribute is populated by model B. So, what you want to do
is:

class B < ActiveRecord::Base

  # id: the id of the record where the text should be stored
  # text: the text to be stored
  def populate_text_field(id, text)
    if a = A.find(id)
      a.update_attribute(:text_field, text)
    end
  end

end

Is this what you are intending?