validates :z, :presence => true, :numericality => {:greater_than => 0}
validates :t, :presence => true, :numericality => {:greater_than_or_equal_to => 0}
+ def self.pickup_item_name
+ Picture.item_name
+ end
+
+ def self.pickup_column_name
+ self.pickup_item_name + '_id'
+ end
+
+ def pickup_id
+ # get :picture_id if head revision
+ self.attributes[self.pickup_column_name]
+ end
+
def attr_y
self.attributes['y']
end