draw datatable is null when i use where in my query - mysql

Question

I have some problem with showing data in datatable, the problem is when I using the query clause like where condition, the draw in datatable is had a null value but when I'm not using the where condition, the data will be display on my datatable, is anything wrong with my query in codeigniter?
model :
var $attendance = 'attendance';
var $employee = 'employee';
var $project = 'project';
var $column = [
null, 'attendance.no_reg', 'employee.name', 'project.project_name', 'project.project_code'
];
var $column_search = [
'attendance.no_reg', 'employee.name', 'project.project_name', 'project.project_code'
];
var $column_order = [
null, 'attendance.no_reg', 'employee.name', 'project.project_name', 'project.project_code'
];
private function _showDaily() {
$selectedValues = $this->input->post('selectedValues');
$this->db->select($this->column);
$this->db->from($this->attendance);
// $this->db->where("project_code", $selectedValues);
$this->db->join($this->employee, "attendance.no_reg = employee.no_reg");
$this->db->join($this->project, "attendance.project_id = project.id");
$this->db->group_by("attendance.no_reg");
// length table
$i = 0;
foreach ($this->column_search as $item) // initial looping for grouping insert a text search
{
error_reporting(0);
if ($_POST['search']['value']) { // if the datatable make a input search with POST method
if ($i === 0) { // initial first condition for first column
$this->db->group_start();
$this->db->like($item, $_POST['search']['value']);
} else {
$this->db->or_like($item, $_POST['search']['value']);
}
if (count($this->column_search) - 1 == $i) // condition if the text search value counting same with $i value then minus 1
$this->db->group_end();
}
$i++;
}
if (isset($_POST['order'])) {
$this->db->order_by($this->column_order[$_POST['order']['0']['column']], $_POST['order']['0']['dir']);
}
}
public function showsDaily()
{
$this->_showDaily();
$result = $this->db->get();
return $result->result();
}
If my explanation is incomprehensible, I apologize, and you can ask me again, Thank You