tetabeer_struct.rb

class User
  include DataMapper::Resource
  
  property :id,         Serial
  property :name,       String
  property :created_at, DateTime
  
  has n, :tags
end

class Tag
  include DataMapper::Resource
  
  property :id,         Serial
  property :created_at, DateTime
  property :updated_at, DateTime
  property :credits,    Integer, :default => 0
  
  belongs_to :user
  has n, :products
  
  def has_credit?
    remaining_credit > 0
  end
  
  def remaining_credit
    self.credits - products_value
  end
  
  def products_value
    value = 0
    self.products.each do |product|
      value += product.value
    end
    return value
  end
end

class Product
  include DataMapper::Resource
  
  property :id,         Serial
  property :name,       String
  property :created_at, DateTime
  property :value,      Integer, :default=>1

  validates_present :name
  
  belongs_to :user
end