Failing test: UoW unable to break cycles when removing entities without DB-level cascade

tests/Tests/ORM/Functional/Ticket/GH5665CommitOrderTest.php

@@ -0,0 +1,116 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Doctrine\Tests\ORM\Functional\Ticket;
+
+use Doctrine\Common\Collections\ArrayCollection;
+use Doctrine\Common\Collections\Collection;
+use Doctrine\ORM\Mapping as ORM;
+use Doctrine\Tests\OrmFunctionalTestCase;
+
+/**
+ * Here, we have a cyclic dependency between entities, but all associations are nullable.
+ * But, we don't have "SET NULL" cascade operations defined at the database level.
+ *
+ * The ORM is able to perform the INSERT operation, since it can NULL out associations
+ * and schedule deferred updates to break the cycles.
+ *
+ * However, it is unable to DELETE the entities. For pending deletions, associations are _not_
+ * first UPDATEd to be NULL in the database before the delete happens.
+ *
+ * By adding ON CASCADE SET NULL (pushing the problem to the DB level explicitly) it will work.
+ */
+final class GH5665CommitOrderTest extends OrmFunctionalTestCase
+{
+    protected function setUp(): void
+    {
+        parent::setUp();
+
+        $this->setUpEntitySchema([GH5665CommitOrderItem::class, GH5665CommitOrderSubitem::class]);
+    }
+
+    public function testIssue(): void
+    {
+        $item = new GH5665CommitOrderItem();
+        $sub1 = new GH5665CommitOrderSubitem();
+        $sub2 = new GH5665CommitOrderSubitem();
+        $item->addItem($sub1);
+        $item->addItem($sub2);
+        $item->featuredItem = $sub2;
+        $this->_em->persist($item);
+        $this->_em->flush();
+
+        $this->expectNotToPerformAssertions();
+
+        $this->_em->remove($item);
+        $this->_em->flush();
+    }
+}
+
+/**
+ * @ORM\Entity
+ */
+class GH5665CommitOrderItem
+{
+    /**
+     * @ORM\Column(name="id", type="integer")
+     * @ORM\Id
+     * @ORM\GeneratedValue(strategy="AUTO")
+     *
+     * @var int
+     */
+    public $id;
+
+    /**
+     * @ORM\OneToMany(targetEntity="GH5665CommitOrderSubitem", mappedBy="item", cascade={"all"}, orphanRemoval=true)
+     *
+     * @var Collection
+     */
+    public $items;
+
+    /**
+     * @ORM\ManyToOne(targetEntity="GH5665CommitOrderSubitem")
+     *
+     * Adding the following would make the test pass, since it shifts responsibility for
+     * NULLing references to the DB layer. The #5665 issue is about the request that this
+     * happen on the ORM level.
+     * > @-ORM\JoinColumn(onDelete="SET NULL")
+     *
+     * @var GH5665CommitOrderSubitem
+     */
+    public $featuredItem;
+
+    public function __construct()
+    {
+        $this->items = new ArrayCollection();
+    }
+
+    public function addItem(GH5665CommitOrderSubitem $item)
+    {
+        $this->items[] = $item;
+        $item->item = $this;
+    }
+}
+
+/**
+ * @ORM\Entity
+ */
+class GH5665CommitOrderSubitem
+{
+    /**
+     * @ORM\Column(name="id", type="integer")
+     * @ORM\Id
+     * @ORM\GeneratedValue(strategy="AUTO")
+     *
+     * @var integer
+     */
+    public $id;
+
+    /**
+     * @var GH5665CommitOrderItem
+     *
+     * @ORM\ManyToOne(targetEntity="GH5665CommitOrderItem", inversedBy="items")
+     */
+    public $item;
+}