var_dump的null值

Question

我得到第一个var_dump的期望值，但是在提交表单时var_dump都得到一个空值。任何人都可以帮我这个吗？ 确切地说，当表单未提交时，我能够获得get-＆gt; trail-＆gt; id的所需结果，但是一旦我完成表单并提交它，$ id的值被指定为null

public function trail_cat_cost($trail_unique_code = null)
{
    if($this->userlib->isLoggedIn())
    {   
        $code = $trail_unique_code;
        $user_id = $this->userlib->getId();
        $id = $this->seller_store_model->get_trail_id($code, $user_id);
        var_dump($id);
        $choice = $this->input->post("travel_cat");
        if(is_null($choice))
        {
            $choice = array();
        }
        $travel_cat = implode(',', $choice);
        $choice1 = $this->input->post("travel_subcat");
        if(is_null($choice1))
        {
            $choice1 = array();
        }
        $travel_subcat = implode(',', $choice1);

        $trail_currency = $this->input->post('trail_currency');
        $trail_cost = $this->input->post('trail_cost');
        $cost_valid_from = $this->input->post('cost_valid_from');
        $cost_valid_upto = $this->input->post('cost_valid_upto');

        //$this->form_validation->set_rules('travel_cat', 'Travel Category', 'trim|required');
        //$this->form_validation->set_rules('travel_subcat', 'Travel Subcategory', 'trim|required');
        $this->form_validation->set_rules('trail_currency', 'Trail Currency', 'trim|required');
        $this->form_validation->set_rules('trail_cost', 'Trail Cost', 'trim|required');
        $this->form_validation->set_rules('cost_valid_from', 'Cost Valid From', 'trim|required');
        $this->form_validation->set_rules('cost_valid_upto', 'Cost Valid Upto', 'trim|required');

        if($this->form_validation->run() == FALSE)
        {   
            $this->load->view('trail_cat_cost');
        }
        else
        {   
            var_dump($id);
            $this->seller_store_model->trail_cat_cost($user_id, $id, $travel_cat, $travel_subcat, $trail_currency, $trail_cost, $cost_valid_from, $cost_valid_upto);
            echo "success";
            //redirect('/seller_store/trail_overview/'.$date);
        }
    }
    else
    {
        echo "User not authorised";
    }
}

评论中的模型代码

public function get_trail_id($code, $user_id) { 

 $query = $this->db->query("SELECT id FROM trail_basic_info WHERE trail_unique_code = '$code' AND user_id = '$user_id'"); foreach($query->result() as $row) { $id = $row->id; $data = array('trail_id'=>$id); $this->db->update($this->search, $data, array('trail_unique_code'=>$code, 'user_id'=>$user_id)); return $row->id; 

}