[php] Codeigniter unset session

Hi I have a site develop in CodeIgniter.

In one of my page I'm using pagination of CodeIgniter after a search form.

In this case I store into my session the search value passed by $_POST because if I have more result clicking the next page the search keppe the searching value.

But when I change page for example I want to return to the index and after return to my search form page the session is already created and make the query with the value of the session. How can I destroy or unset the value of the session when I change page? Is this possible?

Into my model function I check if the session value is different from 0 and exist, if true I make a query with the session value.

This is my controller (nation is the value to store into the session)

public function region_list(){
        $this->load->model('backend/Nation_model');
        $this->load->library("pagination");

        if($_POST)
        {
            if (isset($_POST['ricerca'])){

                $nation = $this->input->post('nation');
                if(strlen($nation) > 0){
                   $this->session->set_userdata('nation',$nation);
                }

                $config = array();
                $config["base_url"] = base_url() . "index.php/backend/region/region_list";
                $config["total_rows"] = $this->Region_model->countRegionSearch();
                $config["per_page"] = 10;
                $config["uri_segment"] = 4;

                $this->pagination->initialize($config);

                $page = ($this->uri->segment(4)) ? $this->uri->segment(4) : 0;
                $data["regionlist"] = $this->Region_model->regionSearch($config["per_page"], $page);
                $data["links"] = $this->pagination->create_links();
                $data["nationlist"] = $this->Nation_model->nationList();

                $this->load->view('backend/region_list_view',$data);
            }
        }
        else
        {
            $config = array();
            $config["base_url"] = base_url() . "index.php/backend/region/region_list";
            $config["total_rows"] = $this->Region_model->countRegion();
            $config["per_page"] = 10;
            $config["uri_segment"] = 4;

            $this->pagination->initialize($config);

            $page = ($this->uri->segment(4)) ? $this->uri->segment(4) : 0;
            $data["links"] = $this->pagination->create_links();
            $data["regionlist"] = $this->Region_model->regionList($config["per_page"], $page);
            $data["nationlist"] = $this->Nation_model->nationList();

            $this->load->view('backend/region_list_view',$data);
        }
    }

and this is my model to search:

function regionList($limit=null, $start=null) {
        $nation_id = $this->session->userdata('nation');
        if ($this->session->userdata('language')=="it")
            $this->db->select('region.id, region.name_it as name,nation.id as nation_id, nation.name_it as nation_name');
        if ($this->session->userdata('language')=="en")
            $this->db->select('region.id, region.name_en as name,nation.id as nation_id, nation.name_en as nation_name');
        $this->db->from('region');
        $this->db->join('nation', 'region.nation_id = nation.id','left');
        if((isset($nation_id))&&($nation_id!=0))
            $this->db->where('region.nation_id', $nation_id);
        $this->db->order_by("name", "asc");
        $this->db->limit($limit, $start);
        $query = $this->db->get();
        $region = array();
        foreach ($query->result() as $row)
            array_push($region, $row);

        return $region;     
    }

    function countRegion() {
        $nation_id = $this->session->userdata('nation');
        if ($this->session->userdata('language')=="it")
            $this->db->select('region.id, region.name_it as name,nation.id as nation_id, nation.name_it as nation_name');
        if ($this->session->userdata('language')=="en")
            $this->db->select('region.id, region.name_en as name,nation.id as nation_id, nation.name_en as nation_name');
        $this->db->from('region');
        $this->db->join('nation', 'region.nation_id = nation.id','left');
        if((isset($nation_id))&&($nation_id!=0))
            $this->db->where('region.nation_id', $nation_id);
        $this->db->order_by("name", "asc");
        $query = $this->db->get();
        return $query->num_rows();  
    }

    public function regionSearch($limit=null, $start=null){
        $nation_id = $this->session->userdata('nation');
        if ($this->session->userdata('language')=="it"){
            $this->db->select('*,region.id, region.name_it as name,nation.id as nation_id, nation.name_it as nation_name');
            if($this->input->post('name')!="")
                $this->db->where('region.name_it LIKE "%'.$this->input->post('name').'%"');
        }

        if ($this->session->userdata('language')=="en"){
            $this->db->select('*,region.id, region.name_en as name,nation.id as nation_id, nation.name_en as nation_name');
            if($this->input->post('name')!="")
                $this->db->where('region.name_en LIKE "%'.$this->input->post('name').'%"');
        }
        $this->db->from('region');
        $this->db->join('nation', 'region.nation_id = nation.id','left');
        if((isset($nation_id))&&($nation_id!=0))
            $this->db->where('region.nation_id', $nation_id);
        $this->db->order_by("name", "asc");
        $this->db->limit($limit, $start);
        $query = $this->db->get();
        $region = array();
        foreach ($query->result() as $row)
            array_push($region, $row);

        return $region; 
     }

     public function countRegionSearch(){
        $nation_id = $this->session->userdata('nation');
        if ($this->session->userdata('language')=="it"){
            $this->db->select('*,region.id, region.name_it as name,nation.id as nation_id, nation.name_it as nation_name');
            if($this->input->post('name')!="")
                $this->db->where('region.name_it LIKE "%'.$this->input->post('name').'%"');
        }

        if ($this->session->userdata('language')=="en"){
            $this->db->select('*,region.id, region.name_en as name,nation.id as nation_id, nation.name_en as nation_name');
            if($this->input->post('name')!="")
                $this->db->where('region.name_en LIKE "%'.$this->input->post('name').'%"');
        }
        $this->db->from('region');
        $this->db->join('nation', 'region.nation_id = nation.id','left');
        if((isset($nation_id))&&($nation_id!=0))
            $this->db->where('region.nation_id', $nation_id);
        $this->db->order_by("name", "asc");

        $query = $this->db->get();
        return $query->num_rows();      
     }

$this->session->unset_userdata('session_value');

Instead of use set_userdata you should use set_flashdata.

According to CI user guide:

CodeIgniter supports "flashdata", or session data that will only be available for the next server request, and are then automatically cleared. These can be very useful, and are typically used for informational or status messages (for example: "record 2 deleted").

http://ellislab.com/codeigniter/user-guide/libraries/sessions.html

I use the old PHP way..It unsets all session variables and doesn't require to specify each one of them in an array. And after unsetting the variables we destroy the session

$session_data = array('username' =>"shashikant");
$this->session->set_userdata('logged_in', $session_data);

$this->session->unset_userdata('logged_in');

I use the old PHP way..It unsets all session variables and doesn't require to specify each one of them in an array. And after unsetting the variables we destroy the session.

session_unset();
session_destroy();