阻止 Doctrine/Symfony 在 foreach 期间加载关联实体?(延迟加载不会发生) [英] Stop Doctrine / Symfony from loading associated entities during foreach? (lazy loading not happening)
问题描述
我看到教义会生成额外的查询来加载我没有直接访问的实体.我认为延迟加载意味着这些关联实体不会被加载.你能帮我弄清楚为什么会发生这些查询以及如何阻止它们吗?
I'm seeing doctrine generating additional queries to load entities that I'm not directly accessing. I thought that lazy loading meant these associate entities wouldn't get loaded. Can you help me figure out why the queries are happening and how to stop them?
这里是有问题的实体:
class Invoice
{
/**
* @ORMOneToMany(targetEntity="InvoiceCard", mappedBy="invoice")
*/
protected $cards;
...
}
class BaseInvoiceCard
{
/**
* @var integer
*
* @ORMColumn(name="id", type="integer")
* @ORMId
* @ORMGeneratedValue(strategy="AUTO")
*/
private $id;
/**
* @var integer
*
* @ORMManyToOne(targetEntity="Invoice", inversedBy="cards")
* @ORMJoinColumn(name="invoice_id", referencedColumnName="id")
*/
protected $invoice;
/**
* @var integer
*
* @ORMManyToOne(targetEntity="Printing")
* @ORMJoinColumn(name="printing_id", referencedColumnName="id")
*/
protected $printing;
...
}
class InvoiceCard extends BaseInvoiceCard{ ... }
class Printing{ ... }
这行代码不会对 InvoiceCards 表产生任何查询:
This line of code doesn't cause any queries to the InvoiceCards table:
$cards = $invoice->getCards();
一旦我这样做:
foreach($cards as $card){
//do nothing in this loop
}
我收到了SELECT ... FROM invoicecard"，这是预期的.
I get a "SELECT ... FROM invoicecard", which is expected.
然而，对于 $cards 中的每张 $card，我也会得到一个SELECT ... FROM printing".我从不调用 $card->getPrinting().即使我在循环内什么都不做也会发生这种情况；只是运行它会导致教义运行这些查询.
However, I'm also getting a "SELECT ... FROM printing" for every $card in $cards. I never call $card->getPrinting(). This happens even if I do nothing at all inside the loop; just running it causes doctrine to run these queries.
为什么会发生这种情况，我该如何预防?
Why this happening and how can I prevent it?
这是 getCards() 的代码.
This is the code for getCards().
/**
* Get cards
*
* @return DoctrineCommonCollectionsCollection
*/
public function getCards()
{
return $this->cards;
}
编辑 2:我找到了解决这个问题的方法，尽管从长远来看它不会解决问题.我将 InvoiceCards 作为数组获取，而不是让学说将它们作为实体进行水合.
EDIT 2: I've found a workaround to this problem, though it's not going to solve things in the long run. I fetch the InvoiceCards as an array, rather than having doctrine hydrate them as entities.
$query->getArrayResult();
在我目前的情况下，无论如何这种技术更好，因为我不需要完全补水的开销.
In my current situation, this technique is better anyways, since I don't require the overhead of full hydration.
但是，该应用程序将在许多地方使用 InvoiceCards，那么原来的问题仍然是一个问题.我觉得要么我误解了 Doctrine 的延迟加载，要么它没有按预期工作.
However, the application will be working with InvoiceCards in many places, and the original issue will be still be a problem then. I feel like either I've misunderstood Doctrine's lazy loading, or it isn't working as expected.
推荐答案
实体正在急切地加载，因为 Printing 是一个父类，其子类使用单表继承.
The entities were getting eagerly loaded because Printing is a parent class whose children use single table inheritance.
如果我将 $printing 更改为指向叶实体，延迟加载将按需要工作.
If I change $printing to point to leaf entity, lazy loading works as desired.
来自 Doctrine 文档，7.2.2.性能影响
From the Doctrine docs, 7.2.2. Performance impact
单表继承有一个一般的性能考虑:如果多对一或一对一关联的目标实体是 STI 实体，出于性能原因，它最好是叶实体在继承层次结构中，(即没有子类).否则，Doctrine不能创建该实体的代理实例，并将总是急切地加载该实体.
There is a general performance consideration with Single Table Inheritance: If the target-entity of a many-to-one or one-to-one association is an STI entity, it is preferable for performance reasons that it be a leaf entity in the inheritance hierarchy, (ie. have no subclasses). Otherwise Doctrine CANNOT create proxy instances of this entity and will ALWAYS load the entity eagerly.
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