yii\db\BaseActiveRecord::__unset PHP Method

    public function __unset($name)
    {
        if ($this->hasAttribute($name)) {
            unset($this->_attributes[$name]);
        } elseif (array_key_exists($name, $this->_related)) {
            unset($this->_related[$name]);
        } elseif ($this->getRelation($name, false) === null) {
            parent::__unset($name);
        }
    }