检索实体集合的最佳做法是什么DISTINCT COUNT？
在此示例实体 ( Customer) 中，我oneToMany与 有关系Orders。
我想计算客户订购了多少销售额和产品：
> select * from orders;
+----------+----------+----------+
| customer | sale_ref | prod_ref |
+----------+----------+----------+
| 1 | sale_1 | prod_1 |
| 1 | sale_1 | prod_2 |
| 1 | sale_2 | prod_1 |
| 1 | sale_3 | prod_3 |
+----------+----------+----------+
> select count(prod_ref) from order where customer = 1;
+-----------------+
| count(prod_ref) |
+-----------------+
| 4 |
+-----------------+
> select count(distinct(sale_ref)) from order where customer = 1;
+-----------------+
| count(prod_ref) |
+-----------------+
| 3 |
+-----------------+
这是代码
use Doctrine\ORM\Mapping as ORM;
class Customer
{
/**
* @var \Doctrine\Common\Collections\Collection
* @ORM\OneToMany(targetEntity="Orders", mappedBy="customer", cascade={"persist", "remove"}, fetch="EXTRA_LAZY")
*/
protected $orders;
/**
* @return \Doctrine\Common\Collections\Collection
*/
public function getOrders(): \Doctrine\Common\Collections\Collection
{
return $this->orders;
}
/**
* @return int
*/
public function getOrdersProductCount(): int
{
return $this->orders->count();
}
}
class Orders
{
/**
* @var Customer $customer
* @ORM\ManyToOne(targetEntity="Customer", inversedBy="orders")
*/
protected $customer;
/**
* Non-unique sales reference
* @var string $salesRef
* @ORM\Column(name="sales_ref", type="string")
*/
protected $salesRef;
使用该Customer->getOrdersProductCount()作品非常适合检索产品数量，据说是“良好做法”，因为它不会在完全加载集合时访问数据库：
https://www.doctrine-project.org/projects/doctrine-orm/en/2.7/tutorials/extra-lazy-associations.html
如果您将关联标记为额外惰性，则可以在不触发集合的完整加载的情况下调用集合的以下方法Collection#count()
但是，在此示例中，aCustomer可以有多个产品用于销售 - 其中salesRef是非唯一的。DISTINCT COUNT检索的最佳方法是什么salesRef？
喵喵时光机