public function behaviors()
    {
        return [
        'timestamp' => [
        'class' => 'yiibehaviorsTimestampBehavior',
        'attributes' => [
        ActiveRecord::EVENT_BEFORE_INSERT => ['log_in_time' ],
        ActiveRecord::EVENT_BEFORE_UPDATE => ['log_in_time'],
        ],
        'value' => new Expression('NOW()'),
        ],
        ];
    }