Data insert codeignetter throwing error - codeigniter

Question

PHP Error was encountered Severity: Notice Message: Undefined
property: Registerform::$db Filename: core/Model.php Line Number: 51
controller file:
A PHP Error was encountered
Severity: Notice
Message: Undefined property: Registerform::$db
Filename: core/Model.php
Line Number: 51
controller file:
<?php
class Registerform extends CI_Controller {
function __construct() {
parent::__construct();
$this->load->model('Registerform_model');
}
public function index() {
//$this->load->database();
$this->load->helper("form");
$this->load->library("form_validation");
$this->form_validation->set_rules("first", "First Name","required");
$this->form_validation->set_rules("last", "Last Name","required");
$this->form_validation->set_rules("email", "Email Address","required|valid_email");
$this->form_validation->set_rules("password", "Password","required");
$this->form_validation->set_rules("phone", "Phone Number","required");
$this->form_validation->set_rules("city", "City","required");
$this->form_validation->set_rules("addrss", " Your Address","required");
if ($this->form_validation->run() == false) {
$this->load->view("registerform_view");
} else {
$first = $_POST["first"];
$last = $_POST["last"];
$email = $_POST["email"];
$password = $_POST["password"];
$phone = $_POST["phone"];
$city = $_POST["city"];
$addrss = $_POST["addrss"];
$data = array(
'first'=>$first,
'last'=>$last,
'email'=>$email,
'password'=>$password,
'phone'=>$phone,
'city'=>$city,
'addrss'=>$addrss
);
//$data="insert into address (first_name,last_name,email,password,phone,city,add) values('$first','$last','$email','$password','$phone','$city','$add')";
$gg = $this->Registerform_model->insert_address($data);
echo $gg;
$this->load->view("registerformsuccess");
}
}
}
?>
model file:
<?php
class Registerform_model extends CI_Model {
function __construct() {
parent::__construct();
}
public function insert_address($data){
$this->db->insert("address", $data);
}
}
?>
view file:
<?php
echo validation_errors();
echo form_open("Registerform");
?>
<label for="first">First Name</label>
<input type="text" name="first" id="first"><br>
<label for="last">Last Name</label>
<input type="text" name="last" id="last"><br>
<label for="email">Email Address</label>
<input type="text" name="email" id="email"><br>
<label for="password">Password</label>
<input type="password" name="password" id="password"><br>
<label for="phone">Phone</label>
<input type="text" name="phone" id="phone"><br>
<label for="city">City Name</label>
<input type="text" name="city" id="city"><br>
<label for="addrss">Your Address</label>
<input type="text" name="addrss" id="addrss"><br>
<input type="submit" name="submit" id="submit" value="Submit">
<?php echo form_close(); ?>

Answer 1

<?php
class Registerform_model extends CI_Model {
function __construct() {
parent::__construct();
}
public function insert_address($data){
$this->load->database();
$this->db->insert("address", $data);
}
}
?>
Its work for me now.

Answer 2

You have to load database.
Put this line in model file constructor function:
$this->load->database();