gistfile1.rb

### config.ru

require_relative_fix 'helpers/init'
require_relative_fix 'models/init'

### user_model.rb

helpers do
  def private
    if session[:user_id]
      @current_user = User.get(session[:user_id])
      true
    else
      redirect '/user/login'
    end
  end
end

### category_model.rb

class Category
  include DataMapper::Resource  
  property :id, Serial
  property :name, String

  def transactions
    private
    Transaction.all(:category_id => self.id, :user_id => @current_user.id)
  end
end