Database query bad method

I get following error in Yajra Datatables in google chrome develper tool

BadMethodCallException Method getQuery does not exist.

code: <?php

namespace App\DataTables;

use App\Staff; use App\CompanyGroup; use Yajra\Datatables\Services\DataTable; use DB;

class EmpDataTable extends DataTable {

/**
* Build DataTable class.
*
* @return \Yajra\Datatables\Engines\BaseEngine
*/
public function ajax()
{       
    return $this->datatables->eloquent($this->query())
        ->addColumn('name',function($staffs) {
            return $staffs->firstname;
        })
        ->addColumn('lastname',function($staffs) {
            return $staffs->lastname;               
        })
        ->make(true);
}


/**
* Get the query object to be processed by dataTables.
*
* @return mixed
*/
public function query()
{
    
    
    $query = Staff::get();

//$query = DB::table('staffs')->get();

    return $this->applyScopes($query);
}

/**
* Optional method if you want to use html builder.
*
* @return \Yajra\Datatables\Html\Builder
*/
public function html()
{   
    return $this->builder()
    ->columns([
        'name',         
        'lastname'
    ])
    ->addAction(['width' => '130px']);
}

}

?>