How to add a fuction in a model yii2 - yii2

Question

I have modified my signup form, I add a field that called billCode, so I want add a function to my signForm model to random integer number, I have a function to random integr and I put that into signup form model like this
class SignupForm extends Model {
// ...
// ...
public static function randomNumber()
{
$randBill = '';
for ($i=0; $i < 8; $i++){
$randBill .= mt_rand(0, 9);
}
return $randBill;
}
public function signup()
{
if (!$this->validate()) {
return null;
}
$user = new User();
$user->username = $this->username;
$user->email = $this->email;
$user->setPassword($this->password);
$user->generateAuthKey();
$user->billCode = randomNumber();
return $user->save() ? $user : null;
}
}
when I press the submit button in signUp Form, yii2 keep give me this error
Call to undefined function frontend\models\randomNumber()
Any help?

Answer 1

Copy from comment
randomNumber is a static function, you can't call it just by randomNumber(). Using self::randomNumber() could be work.

Answer 2

You can call it by self keyword
class SignupForm extends Model {
// ...
// ...
public static function randomNumber()
{
$randBill = '';
for ($i=0; $i < 8; $i++){
$randBill .= mt_rand(0, 9);
}
return $randBill;
}
public function signup()
{
if (!$this->validate()) {
return null;
}
$user = new User();
$user->username = $this->username;
$user->email = $this->email;
$user->setPassword($this->password);
$user->generateAuthKey();
//$user->billCode = $this->randomNumber();
$user->billCode = self::randomNumber();
return $user->save() ? $user : null;
}
}