Yii2更新记录时如何忽略ActiveForm中的输入

i have a problem. I have a required field "password". I want to ignore the last field when i clicked on "update" button. Thank you for your attention.

My rules:

 public function rules()
    {
        return [
            [['username', 'role_id', 'surname', 'name', 'patronymic', 'email', 'password', 'department_id'], 'required'],
            [['role_id', 'department_id'], 'integer'],
            [['date_of_birth'], 'safe'],
            [['password'], 'string', 'min' => 8],
            [['username', 'surname', 'name', 'patronymic', 'email', 'telephone', 'skype', 'avatar', 'password'], 'string', 'max' => 255],
            [['role_id'], 'exist', 'skipOnError' => true, 'targetClass' => Roles::className(), 'targetAttribute' => ['role_id' => 'id']],
            [['department_id'], 'exist', 'skipOnError' => true, 'targetClass' => Department::className(), 'targetAttribute' => ['department_id' => 'id']],
            [['file'], 'file', 'extensions' => 'png, jpg'],
            ['email', 'email'],
            [['email', 'username'], 'unique'],
];`

Also in my User models i used BeforeSave function (to hash my password, when i created a new record).

    public function beforeSave($insert)
{
    if (isset($this->password)) {
        $this->password = Yii::$app->getSecurity()->generatePasswordHash($this->password);
    }
    return parent::beforeSave($insert);
}

My controller update action:

    public function actionUpdate($id)
{
    $model = $this->findModel($id);

    if ($model->load(Yii::$app->request->post()) && $model->save()) {

        $imageName = uniqid();
        $model->file = UploadedFile::getInstance($model, 'file');
        if (!empty($model->file)){
            $model->file->saveAs( 'uploads/'.$imageName.'.'.$model->file->extension );
            $model->avatar = 'uploads/'.$imageName.'.'.$model->file->extension;
            $model->save(false);
        }
        return $this->redirect(['view', 'id' => $model->id]);
    } else {
        return $this->render('update', [
            'model' => $model,
        ]);
    }
}

You can use scenarios to do this: docs, but u shouldn't hash password in beforeSave(). Like in advanced template, create setter for password OR create custom filter in rules + add scenario like 'on' => 'createUser' or 'except' => 'updateUser'.