How to assign currently logged in user name to a table field

I have 3 tables
items (columns are: id, name , type)
history(columns are: id, date, username, item_id, user_id)
user(id , username, password)

When a user "ABC" logs in and creates a new item, a history record gets
created with the following after_create filter.
How to set the username field in history table to "ABC".

class Item < ActiveRecord::Base
has_many :histories
after_create :update_history
def update_history
histories.create(:date=>Time.now, username=> ?)
end

My login method in user_controller
def login
      if request.post?
      user=User.authenticate(params[:username])
      if user
        session[:user_id] =user.id
        redirect_to( :action=>'home')
           flash[:message] = "Successfully logged in "
      else
        flash[:notice] = "Incorrect user/password combination"
        redirect_to(:action=>"login")
      end
    end
  end

I am not using any authentication plugin. I would appreciate if someone
could tell me how to achieve this without using plugin(like userstamp
etc.) if possible.

Hi,
If u dont want to use any of the plugin then u need to write ur own
action and need to do manually.

Like:

def current_user
   @current_user = User.find(session[:user_id])
end

Keep this action into ur application controller, It will return u the
current logedin user object.
So u may use this like

def update_history
histories.create(:date=>Time.now, username=> current_user.name)
end

I hope it will work 4 u.
But instead of doing manually I suggest u must use Authlogic gem/plugin
it will gives u other benefits also.