abstract class Entity {

    abstract public function getEntityType() : int;

    public function compareHash(array $dataItem) : bool {

        // todo
        // Return big array from data base
        $hashBase = (new HashBase())->getData($this->getEntityType());

    }

}

abstract class Entity {
    abstract public function getEntityType() : int;
    public static $hashBaseArr = [];

    public function compareHash(array $dataItem) : bool {
        // todo
        // Return big array from data base
        if ( !isset(static::$hashBaseArr[get_called_class()]) ) {
            static::$hashBaseArr[get_called_class()] = (new HashBase())->getData($this->getEntityType());
        }
    }
}