# PUT /users/1
def update
  @user = User.find(params[:id])

  if @user.update_attributes(params[:user])
    if params[:profile][:available] == 1 #available is a checkbox that stores a simple flag in the database.
      @user.create_profile(params[:profile])
    end
  else
    #some warnings and errors
  end
end

Profile.new(:user_id => @user.id)

Profile.create(:user_id => @user.id)

profile = @user.build_profile
profile.save