public function add($conditions, $types = [])
    {
        if (is_string($conditions)) {
            $this->_conditions[] = $conditions;

            return $this;
        }

        if ($conditions instanceof ExpressionInterface) {
            $this->_conditions[] = $conditions;

            return $this;
        }

        $this->_addConditions($conditions, $types);

        return $this;
    }