PHP数据库查询 - 第一次不起作用（CodeIgniter）

Having a nightmare here and can't work out what's wrong. Basically I have a codeigniter setup that is running a couple of database queries but for some reason it doesn't seem to work the first time after a refresh.

So this is what is currently happening: I submit the form and the form data goes in to the database correctly, however the $property_id ends up blank in createInitialTenancy() function and the $tenancy_id ends up blank in the insertBasicInfo() function.

If I then submit the form again (either by submitting without a refresh or by refreshing) then both these values are populated.

Can anyone explain a reason behind this?

Controller:

public function new($property_id) {
  // Check for a property ID. Redirect to dashboard if none present.
  if(!$property_id) {
    redirect(base_url());
  }

  // Check for the form having been submitted
  if ($this->input->post()) {

    // Strip form data for XSS
    $form_data =  $this->security->xss_clean($this->input->post());

    // Create the initial tenancy entry in the database
    $tenancy_data['property_id'] = $property_id;
    $tenancy_id = $this->tenancy_model->createInitialTenancy($tenancy_data);

    // Empty tenant array. We've dealt with this elsewhere
    unset($form_data['tenant']);

    // Insert the data to the tenancy.basic_info database
    $form_data['lead_tenant_id'] = $_SESSION["tenant_id"];
    $form_data['property_id'] = $property_id;
    $form_data['tenancy_id'] = $tenancy_id;

    $this->tenancy_model->insertBasicInfo($form_data);
  }

  // Security token required for the form
  $csrf = array(
    'name' => $this->security->get_csrf_token_name(),
    'hash' => $this->security->get_csrf_hash()
  );

  $this->load->view('header-signin');
  $this->load->view('tenant/tenancy/new', $csrf);
  $this->load->view('footer-signin');
}

Model:

class Tenancy_model extends CI_Model {

  function __construct() {
    $this->load->database();
    parent::__construct();
  }

  public function insertBasicInfo($form_data) {
    $this->db->insert('tenancy_basic_info', $form_data);
  }

  public function createInitialTenancy($data) {
    $this->db->insert('tenancy_tenancy', $data);
    return $this->db->insert_id();
  }

  public function getTenancyByPropertyID($property_id) {
    $this->db->select('id');
    $this->db->from('tenancy_tenancy');
    $this->db->where('property_id', $property_id);
    $tenancy = $this->db->get()->result();
    return $tenancy;
  }
} 

tenancy_tenancy Table:

CREATE TABLE `tenancy_tenancy` (
  `id` int(11) unsigned NOT NULL AUTO_INCREMENT,
  `property_id` int(11) DEFAULT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=59 DEFAULT CHARSET=utf8;

tenancy_basic_info Table:

CREATE TABLE `tenancy_basic_info` (
  `id` int(11) unsigned NOT NULL AUTO_INCREMENT,
  `tenancy_id` int(11) DEFAULT NULL,
  `lead_tenant_id` int(11) NOT NULL,
  `property_id` int(11) NOT NULL,
  `more-tenants` int(11) NOT NULL,
  `pets` int(11) NOT NULL,
  `pets_info` text,
  `cars` int(11) NOT NULL,
  `number_of_cars` int(11) NOT NULL,
  `information` text,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=43 DEFAULT CHARSET=utf8;