public function with($relationships)
    {
        $this->requiredRelationships = [];

        if ($relationships == 'all') {
            $this->requiredRelationships = $this->relationships;
        } elseif (is_array($relationships)) {
            $this->requiredRelationships = array_filter($relationships, function ($value) {
                return in_array($value, $this->relationships);
            });
        } elseif (is_string($relationships)) {
            array_push($this->requiredRelationships, $relationships);
        }

        return $this;
    }