Deprecate undeclared entity inheritance

Inheritance has to be declared as soon as one entity class extends (directly or through middle classes) another one.

This is also pointed out in the opening comment for #8348:

> Entities are not allowed to extend from entities without an inheritence mapping relationship (Single Table or Joined Table inheritance). [...] While Doctrine so far allowed these things, they are fragile and will break on certain scenarios.

Throwing an exception in case of this misconfiguration is nothing we should do light-heartedly, given that it may surprise users in a bugfix or feature release. So, we should start with a deprecation notice  and make this an exception in 3.0. The documentation is updated accordingly at #10429.

Catching missing inheritance declarations early on is important to avoid weird errors further down the road, giving users a clear indication of the root cause.

In case you are affected by this, please understand that although things "previously worked" for you, you have been using the ORM outside of what it was designed to do. That may have worked in simple cases, but may also have caused invalid results (wrong or missing data after hydration?) that possibly went unnoticed in subtle cases.

UPGRADE.md

@@ -12,6 +12,11 @@ now deprecated and will be removed in 3.0.
 
 # Upgrade to 2.14
 
+## Deprecated undeclared entity inheritance
+
+As soon as an entity class inherits from another entity class, inheritance has to 
+be declared by adding the appropriate configuration for the root entity.
+
 ## Deprecated `Doctrine\ORM\Persisters\Exception\UnrecognizedField::byName($field)` method.
 
 Use `Doctrine\ORM\Persisters\Exception\UnrecognizedField::byFullyQualifiedName($className, $field)` instead.

lib/Doctrine/ORM/Mapping/ClassMetadataFactory.php

@@ -148,6 +148,18 @@ protected function doLoadMetadata($class, $parent, $rootEntityFound, array $nonS
         }
 
         if (! $class->isMappedSuperclass) {
+            if ($rootEntityFound && $class->isInheritanceTypeNone()) {
+                Deprecation::trigger(
+                    'doctrine/orm',
+                    'https://github.com/doctrine/orm/pull/10431',
+                    "Entity class '%s' is a subclass of the root entity class '%s', but no inheritance mapping type was declared. This is a misconfiguration and will be an error in Doctrine ORM 3.0.",
+                    $class->name,
+                    end($nonSuperclassParents)
+                );
+                // enable this in 3.0
+                // throw MappingException::missingInheritanceTypeDeclaration(end($nonSuperclassParents), $class->name);
+            }
+
             foreach ($class->embeddedClasses as $property => $embeddableClass) {
                 if (isset($embeddableClass['inherited'])) {
                     continue;

lib/Doctrine/ORM/Mapping/MappingException.php

@@ -539,6 +539,19 @@ static function ($a, $b) {
         );
     }
 
+    /**
+     * @param class-string $rootEntityClass
+     * @param class-string $childEntityClass
+     */
+    //public static function missingInheritanceTypeDeclaration(string $rootEntityClass, string $childEntityClass): self
+    //{
+    //    return new self(sprintf(
+    //        "Entity class '%s' is a subclass of the root entity class '%s', but no inheritance mapping type was declared.",
+    //        $childEntityClass,
+    //        $rootEntityClass
+    //    ));
+    //}
+
     /**
      * @param string $className
      *

tests/Doctrine/Tests/Models/DDC1590/DDC1590Entity.php

@@ -6,13 +6,11 @@
 
 use DateTime;
 use Doctrine\ORM\Mapping\Column;
-use Doctrine\ORM\Mapping\Entity;
 use Doctrine\ORM\Mapping\GeneratedValue;
 use Doctrine\ORM\Mapping\Id;
 use Doctrine\ORM\Mapping\MappedSuperclass;
 
 /**
- * @Entity
  * @MappedSuperclass
  */
 abstract class DDC1590Entity

tests/Doctrine/Tests/Models/DDC2372/DDC2372User.php

@@ -5,15 +5,21 @@
 namespace Doctrine\Tests\Models\DDC2372;
 
 use Doctrine\ORM\Mapping\Column;
+use Doctrine\ORM\Mapping\DiscriminatorColumn;
+use Doctrine\ORM\Mapping\DiscriminatorMap;
 use Doctrine\ORM\Mapping\Entity;
 use Doctrine\ORM\Mapping\GeneratedValue;
 use Doctrine\ORM\Mapping\Id;
+use Doctrine\ORM\Mapping\InheritanceType;
 use Doctrine\ORM\Mapping\Table;
 use Doctrine\Tests\Models\DDC2372\Traits\DDC2372AddressAndAccessors;
 
 /**
  * @Entity
  * @Table(name="users")
+ * @InheritanceType("SINGLE_TABLE")
+ * @DiscriminatorColumn("type")
+ * @DiscriminatorMap({"user"="DDC2372User", "admin"="DDC2372Admin"})
  */
 class DDC2372User
 {

tests/Doctrine/Tests/Models/DDC5934/DDC5934BaseContract.php

@@ -8,13 +8,13 @@
 use Doctrine\Common\Collections\Collection;
 use Doctrine\ORM\Mapping\ClassMetadata;
 use Doctrine\ORM\Mapping\Column;
-use Doctrine\ORM\Mapping\Entity;
 use Doctrine\ORM\Mapping\GeneratedValue;
 use Doctrine\ORM\Mapping\Id;
 use Doctrine\ORM\Mapping\ManyToMany;
+use Doctrine\ORM\Mapping\MappedSuperclass;
 
-/** @Entity */
-#[Entity]
+/** @MappedSuperclass() */
+#[MappedSuperclass]
 class DDC5934BaseContract
 {
     /**

tests/Doctrine/Tests/ORM/Mapping/BasicInheritanceMappingTest.php

@@ -4,6 +4,7 @@
 
 namespace Doctrine\Tests\ORM\Mapping;
 
+use Doctrine\Deprecations\PHPUnit\VerifyDeprecations;
 use Doctrine\ORM\EntityRepository;
 use Doctrine\ORM\Id\SequenceGenerator as IdSequenceGenerator;
 use Doctrine\ORM\Mapping\ClassMetadata;
@@ -29,13 +30,16 @@
 use Doctrine\Tests\Models\DDC869\DDC869Payment;
 use Doctrine\Tests\Models\DDC869\DDC869PaymentRepository;
 use Doctrine\Tests\OrmTestCase;
+use Generator;
 
 use function assert;
 use function serialize;
 use function unserialize;
 
 class BasicInheritanceMappingTest extends OrmTestCase
 {
+    use VerifyDeprecations;
+
     /** @var ClassMetadataFactory */
     private $cmf;
 
@@ -218,6 +222,42 @@ public function testMappedSuperclassIndex(): void
         self::assertArrayHasKey('IDX_MAPPED1_INDEX', $class->table['uniqueConstraints']);
         self::assertArrayHasKey('IDX_MAPPED2_INDEX', $class->table['indexes']);
     }
+
+    /**
+     * @dataProvider invalidHierarchyDeclarationClasses
+     */
+    public function testUndeclaredHierarchyRejection(string $rootEntity, string $childClass): void
+    {
+        $this->expectDeprecationWithIdentifier('https://github.com/doctrine/orm/pull/10431');
+
+        /* on 3.0, use this instead: */
+        // self::expectException(MappingException::class);
+        // self::expectExceptionMessage(\sprintf(
+        //     "Entity class '%s' is a subclass of the root entity class '%s', but no inheritance mapping type was declared.",
+        //     $childClass,
+        //     $rootEntity
+        // ));
+
+         $this->cmf->getMetadataFor($childClass);
+    }
+
+    public function invalidHierarchyDeclarationClasses(): Generator
+    {
+        yield 'concrete Entity root and child class, direct inheritance'
+            => [InvalidEntityRoot::class, InvalidEntityRootChild::class];
+
+        yield 'concrete Entity root and abstract child class, direct inheritance'
+            => [InvalidEntityRoot::class, InvalidEntityRootAbstractChild::class];
+
+        yield 'abstract Entity root and concrete child class, direct inheritance'
+            => [InvalidAbstractEntityRoot::class, InvalidAbstractEntityRootChild::class];
+
+        yield 'abstract Entity root and abstract child class, direct inheritance'
+            => [InvalidAbstractEntityRoot::class, InvalidAbstractEntityRootAbstractChild::class];
+
+        yield 'complex example (Entity Root -> Mapped Superclass -> transient class -> Entity)'
+            => [InvalidComplexRoot::class, InvalidComplexEntity::class];
+    }
 }
 
 class TransientBaseClass
@@ -438,3 +478,85 @@ class MediumSuperclassEntity extends MediumSuperclassBase
 class SubclassWithRepository extends DDC869Payment
 {
 }
+
+/**
+ * @Entity
+ *
+ * This class misses the DiscriminatorMap declaration
+ */
+class InvalidEntityRoot
+{
+    /**
+     * @Column(type="integer")
+     * @Id
+     * @GeneratedValue(strategy="AUTO")
+     * @var int
+     */
+    public $id;
+}
+
+/** @Entity */
+class InvalidEntityRootChild extends InvalidEntityRoot
+{
+}
+
+/** @Entity */
+abstract class InvalidEntityRootAbstractChild extends InvalidEntityRoot
+{
+}
+
+/**
+ * @Entity
+ *
+ * This class misses the DiscriminatorMap declaration
+ */
+class InvalidAbstractEntityRoot
+{
+    /**
+     * @Column(type="integer")
+     * @Id
+     * @GeneratedValue(strategy="AUTO")
+     * @var int
+     */
+    public $id;
+}
+
+/** @Entity */
+class InvalidAbstractEntityRootChild extends InvalidAbstractEntityRoot
+{
+}
+
+/** @Entity */
+abstract class InvalidAbstractEntityRootAbstractChild extends InvalidAbstractEntityRoot
+{
+}
+
+/**
+ * @Entity
+ *
+ * This class misses the DiscriminatorMap declaration
+ */
+class InvalidComplexRoot
+{
+    /**
+     * @Column(type="integer")
+     * @Id
+     * @GeneratedValue(strategy="AUTO")
+     * @var int
+     */
+    public $id;
+}
+
+/** @MappedSuperclass */
+class InvalidComplexMappedSuperclass extends InvalidComplexRoot
+{
+}
+
+class InvalidComplexTransientClass extends InvalidComplexMappedSuperclass
+{
+}
+
+/** @Entity */
+class InvalidComplexEntity extends InvalidComplexTransientClass
+{
+}