Make it possible to have non-NULLable self-referencing associations when using application-provided IDs

The change makes the `BasicEntityPersister` not schedule an extra update in the case of an entity referencing itself and having an application-provided ID (the "NONE" generator strategy).

While it looks like a special corner case, the INSERTion of a NULL value plus the extra update require the self-referencing column to be defined as NULLable. This is only an issue for the self-referencing entity case. All other associations work naturally.

Fixes #7877, closes #7882.

Co-authored-by: Sylvain Fabre <sylvain.fabre@assoconnect.com>

Author: mpdude

lib/Doctrine/ORM/Persisters/Entity/BasicEntityPersister.php

@@ -683,7 +683,17 @@ protected function prepareUpdateData($entity, bool $isInsert = false)
             if ($newVal !== null) {
                 $oid = spl_object_id($newVal);
 
-                if (isset($this->queuedInserts[$oid]) || $uow->isScheduledForInsert($newVal)) {
+                if ($newVal === $entity && $this->class->isIdentifierNatural()) {
+                    // When the associated entity is in fact the entity itself (= we have a
+                    // self-referencing entity), and the ID has already been provided by the
+                    // application, then we can INSERT all the data right away and need not
+                    // schedule the extra update. Due to the "references itself" condition,
+                    // this looks like a very special case. But, in fact, this is the
+                    // corner case that makes it possible to define such self-referencing
+                    // columns as not-NULLable when using application-side ID generators.
+
+                    // do nothing
+                } elseif (isset($this->queuedInserts[$oid]) || $uow->isScheduledForInsert($newVal)) {
                     // The associated entity $newVal is not yet persisted, so we must
                     // set $newVal = null, in order to insert a null value and schedule an
                     // extra update on the UnitOfWork.

tests/Doctrine/Tests/ORM/Functional/GH7877Test.php

@@ -0,0 +1,60 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Doctrine\Tests\ORM\Functional;
+
+use Doctrine\ORM\Mapping as ORM;
+use Doctrine\Tests\OrmFunctionalTestCase;
+
+use function uniqid;
+
+/**
+ * @group GH7877
+ */
+class GH7877Test extends OrmFunctionalTestCase
+{
+    protected function setUp(): void
+    {
+        parent::setUp();
+
+        $this->createSchemaForModels(
+            GH7877ApplicationGeneratedIdEntity::class
+        );
+    }
+
+    public function testSelfReferenceWithApplicationGeneratedIdMayBeNotNullable(): void
+    {
+        $entity         = new GH7877ApplicationGeneratedIdEntity();
+        $entity->id     = uniqid();
+        $entity->parent = $entity;
+
+        $this->expectNotToPerformAssertions();
+
+        $this->_em->persist($entity);
+        $this->_em->flush();
+    }
+}
+
+/**
+ * @ORM\Entity
+ */
+class GH7877ApplicationGeneratedIdEntity
+{
+    /**
+     * @ORM\Id
+     * @ORM\Column(type="string")
+     * @ORM\GeneratedValue(strategy="NONE")
+     *
+     * @var string
+     */
+    public $id;
+
+    /**
+     * @ORM\ManyToOne(targetEntity="GH7877ApplicationGeneratedIdEntity")
+     * @ORM\JoinColumn(name="parent_id", referencedColumnName="id", nullable=false)
+     *
+     * @var self
+     */
+    public $parent;
+}