public function buildQuery()
    {
        $model = $this->model;
        $query = $model::query();

        // perform joins
        if (is_array($this->join)) {
            foreach ($this->join as $condition) {
                list($joinModel, $column, $foreignKey) = $condition;
                $query->join($joinModel, $column, $foreignKey);
            }
        }

        // sanitze and set the filter
        $filter = $this->parseFilterInput($this->filter);
        $query->where($filter);

        // performs a search using LIKE queries
        // WARNING use sparingly, these queries are expensive
        if (!empty($this->search) && is_string($this->search) && property_exists($model, 'searchableProperties')) {
            $w = [];
            $search = addslashes($this->search);
            foreach ($model::$searchableProperties as $name) {
                $w[] = "`$name` LIKE '%$search%'";
            }

            if (count($w) > 0) {
                $query->where('('.implode(' OR ', $w).')');
            }
        }

        // eager loading
        foreach ($this->expand as $k) {
            $property = $model::getProperty($k);
            if ($property && isset($property['relation'])) {
                if (isset($property['id_property'])) {
                    $query->with($property['id_property']);
                } else {
                    $query->with($k);
                }
            }
        }

        if (isset($this->sort)) {
            $query->sort($this->sort);
        }

        // calculate limit and offset
        $start = ($this->page - 1) * $this->perPage;
        $query->start($start)->limit($this->perPage);

        return $query;
    }