Laravel Eloquent：从子查询创建自定义属性

Question

模态：Subscription.php

class Subscription extends Model {
   use HasFactory;

   public function payments(): HasMany {
      return $this->hasMany(SubscriptionPayment::class, 'sub_id');
   }

   public function totalDurationDays(): Attribute {
      return Attribute::make(
         get: fn() => $this->payments()->sum('duration_days')
      )->shouldCache();
   }
}

控制器：SubscriptionController.php

    $subs = SharedServer::from('subscriptions AS ss')
       ->select(
          'ss.*',
          DB::raw("(SELECT SUM(duration_days) FROM subscription_payments AS ssp WHERE ssp.sub_id = ss.id) AS total_duration_days"),
       )
       ->paginate();

如果从自定义属性调用

total_duration_days

，与直接从控制器调用相比，Laravel 调试栏会显示太多查询。

有没有一种方法可以指示查询构建器直接在一个查询中立即加载

total_duration_days

自定义属性？

Answer 1

如果您想使用totalDurationDays方法作为自定义属性并避免多次查询，则需要立即加载付款关系。这样，可以从加载的付款集合中计算总和，而不是针对每个订阅模型进行额外的查询。

在你的 subscriptioncontroller.php 中

// Eager load payments relationship
$subs = SharedServer::from('subscriptions AS ss')
    ->with('payments')
    ->paginate();`