models:

public function Fields()
{
　　$fields = parent::Fields();//原来models输出字段

　$fields['parentComment'] = function (self $model){//‘parentComment’自定义输出字段

　　return ShopComment::find()->select('content')->where(['parent_id'=>$model->comment_id])->One();//列子是 查找评论父级数据；
};

return $fields;
}

controller:

$models = shopComment::find()->where(['comment_id'=>6])->One();
$models = $models->toArray();