private function _checkOnArguments(array $firstColumn, array $secondColumn)
	{
		if(!array_key_exists('column', $firstColumn) || !array_key_exists('table', $firstColumn) ||
		   !array_key_exists('column', $secondColumn) || !array_key_exists('table', $secondColumn)
		)
		{
			throw new \InvalidArgumentException('Both arguments of on method require "column" and "table" as key');
		}
	}