public function getComputedColumns()
	{
		//make sure we only run this once and then return the cached version
		if (!sizeof($this->computedColumns))
		{
			foreach ($this->getColumns() as $column)
			{
				if (!$column->getOption('is_related') && $column->getOption('is_computed'))
				{
					$this->computedColumns[$column->getOption('column_name')] = $column->getOption('column_name');
				}
			}
		}

		return $this->computedColumns;
	}