code: public function getElement($fieldName, $uniqueValue, $contentId = null)
      {
          $element = null;
  
          if (!$contentId)
          {
              $contentId = $this->content_id;
          }
  
          if (strpos("field_" . $fieldName, 'element.'))
          {
              $realName = str_replace("element.", "", $fieldName);
              $element = CmsContentElement::find()->where([$realName => $uniqueValue])->one();
  
          } else if (strpos("field_" . $fieldName, 'property.'))
          {
              $realName = str_replace("property.", "", $fieldName);
  
              /**
               * @var $property CmsContentProperty
               */
              $property = CmsContentProperty::find()->where(['code' => $realName])->one();
              $query = CmsContentElement::find();
              CmsContentElement::filterByProperty($query, $property, $uniqueValue);
  
              //print_r($query->createCommand()->rawSql);die;
              $element = $query->one();
          }
  
          return $element;
      }
docs: @param $fieldName
  @param $uniqueValue
  @param null $contentId
  
  @return array|null|\yii\db\ActiveRecord