试图获取非对象Yii2 ActiveRecord的属性

Question

我正在开发Yii2并遇到一些问题。 这是代码：

$conditionSymptom = ConditionSymptom::find()->where([
        'condition_id' => $this->id,
        'symptom_id' => $symptomId,
        'age_group_id' => $ageGroupId,
        'gender_id' => $genderId,
    ])->one();
echo $conditionSymptom->condition_id;  // error 'Trying to get property of non-object' is here

var_dump($conditionSymptom);显示：

string(5) "
"
object(common\models\SC\ConditionSymptom)#196 (8) {
  ["_attributes":"yii\db\BaseActiveRecord":private]=>
  array(7) {
    ["id"]=>
    int(176)
    ["condition_id"]=>
    int(5)
    ["symptom_id"]=>
    int(35)
    ["age_group_id"]=>
    int(10)
    ["possibility"]=>
    int(11)
    ["gender_id"]=>
    int(1)
    ["sort_value"]=>
    int(1011)
  }
  ["_oldAttributes":"yii\db\BaseActiveRecord":private]=>
  array(7) {
    ["id"]=>
    int(176)
    ["condition_id"]=>
    int(5)
    ["symptom_id"]=>
    int(35)
    ["age_group_id"]=>
    int(10)
    ["possibility"]=>
    int(11)
    ["gender_id"]=>
    int(1)
    ["sort_value"]=>
    int(1011)
  }
  ["_related":"yii\db\BaseActiveRecord":private]=>
  array(0) {
  }
  ["_errors":"yii\base\Model":private]=>
  NULL
  ["_validators":"yii\base\Model":private]=>
  NULL
  ["_scenario":"yii\base\Model":private]=>
  string(7) "default"
  ["_events":"yii\base\Component":private]=>
  array(0) {
  }
  ["_behaviors":"yii\base\Component":private]=>
  array(0) {
  }
}
string(6) "
" 

var_dump表明$conditionSymptom是对象，我不明白为什么会出现错误。

请帮助解决此问题。