himiklab\sortablegrid\SortableGridBehavior::beforeInsert PHP Method

    public function beforeInsert()
    {
        /** @var ActiveRecord $model */
        $model = $this->owner;
        if (!$model->hasAttribute($this->sortableAttribute)) {
            throw new InvalidConfigException("Invalid sortable attribute `{$this->sortableAttribute}`.");
        }
        $query = $model::find();
        if (is_callable($this->scope)) {
            call_user_func($this->scope, $query);
        }
        $maxOrder = $query->max('{{' . trim($model::tableName(), '{}') . '}}.[[' . $this->sortableAttribute . ']]');
        $model->{$this->sortableAttribute} = $maxOrder + 1;
    }