Rework association mapping hierarchy

- Each type is now either final, abstract or an interface.
- The mappedBy attribute is no longer nullable and moved down the
  hierarchy.
- The inversedBy attribute is still nullable and also moved down the
  hierarchy.
- Code common to ManyToOneAssociationMapping and
  OneToOneOwningSideMapping is de-duplicated and moved up the hierarchy
- Code inside ToManyInverseSideMapping and ToManyOwningSideMapping comes
  from a trait to avoid duplication.

lib/Doctrine/ORM/Internal/Hydration/ObjectHydrator.php

@@ -83,7 +83,7 @@ protected function prepare(): void
             }
 
             // Mark any non-collection opposite sides as fetched, too.
-            if ($assoc['mappedBy']) {
+            if (! $assoc->isOwningSide()) {
                 $this->hints['fetched'][$dqlAlias][$assoc['mappedBy']] = true;
 
                 continue;
@@ -439,7 +439,7 @@ protected function hydrateRowData(array $row, array &$result): void
                                         $targetClass->reflFields[$inverseAssoc['fieldName']]->setValue($element, $parentObject);
                                         $this->uow->setOriginalEntityProperty(spl_object_id($element), $inverseAssoc['fieldName'], $parentObject);
                                     }
-                                } elseif ($parentClass === $targetClass && $relation['mappedBy']) {
+                                } elseif ($parentClass === $targetClass && ! $relation->isOwningSide()) {
                                     // Special case: bi-directional self-referencing one-one on the same class
                                     $targetClass->reflFields[$relationField]->setValue($element, $parentObject);
                                 }

lib/Doctrine/ORM/Mapping/AssociationMapping.php

@@ -17,22 +17,6 @@
 /** @template-implements ArrayAccess<string, mixed> */
 abstract class AssociationMapping implements ArrayAccess
 {
-    /**
-     * required for bidirectional associations
-     * The name of the field that completes the bidirectional association on
-     * the owning side. This key must be specified on the inverse side of a
-     * bidirectional association.
-     */
-    public string|null $mappedBy = null;
-
-    /**
-     * required for bidirectional associations
-     * The name of the field that completes the bidirectional association on
-     * the inverse side. This key must be specified on the owning side of a
-     * bidirectional association.
-     */
-    public string|null $inversedBy = null;
-
     /**
      * The names of persistence operations to cascade on the association.
      *
@@ -159,12 +143,12 @@ public static function fromMappingArray(array $mappingArray): static
     }
 
     /**
-     * @psalm-assert-if-true AssociationOwningSideMapping $this
-     * @psalm-assert-if-false string $this->mappedBy
+     * @psalm-assert-if-true OwningSideMapping $this
+     * @psalm-assert-if-false InverseSideMapping $this
      */
     final public function isOwningSide(): bool
     {
-        return $this instanceof AssociationOwningSideMapping;
+        return $this instanceof OwningSideMapping;
     }
 
     /** @psalm-assert-if-true ToOneAssociationMapping $this */
@@ -335,8 +319,6 @@ public function __sleep(): array
 
         foreach (
             [
-                'mappedBy',
-                'inversedBy',
                 'fetch',
                 'inherited',
                 'declared',

lib/Doctrine/ORM/Mapping/ClassMetadata.php

@@ -1392,13 +1392,7 @@ protected function _validateAndCompleteAssociationMapping(array $mapping): Assoc
                         $this->table ?? null,
                         $this->isInheritanceTypeSingleTable(),
                     ) :
-                    OneToOneAssociationMapping::fromMappingArrayAndName(
-                        $mapping,
-                        $this->namingStrategy,
-                        $this->name,
-                        $this->table,
-                        $this->isInheritanceTypeSingleTable(),
-                    );
+                    OneToOneInverseSideMapping::fromMappingArrayAndName($mapping, $this->name);
 
             case self::MANY_TO_ONE:
                 return ManyToOneAssociationMapping::fromMappingArrayAndName(
@@ -1419,7 +1413,7 @@ protected function _validateAndCompleteAssociationMapping(array $mapping): Assoc
 
                 return $mapping['isOwningSide'] ?
                     ManyToManyOwningSideMapping::fromMappingArrayAndNamingStrategy($mapping, $this->namingStrategy) :
-                    ManyToManyAssociationMapping::fromMappingArray($mapping);
+                    ManyToManyInverseSideMapping::fromMappingArray($mapping);
 
             default:
                 throw MappingException::invalidAssociationType(

lib/Doctrine/ORM/Mapping/InverseSideMapping.php

@@ -0,0 +1,30 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Doctrine\ORM\Mapping;
+
+abstract class InverseSideMapping extends AssociationMapping
+{
+    /**
+     * required for bidirectional associations
+     * The name of the field that completes the bidirectional association on
+     * the owning side. This key must be specified on the inverse side of a
+     * bidirectional association.
+     */
+    public string $mappedBy;
+
+    final public function backRefFieldName(): string
+    {
+        return $this->mappedBy;
+    }
+
+    /** @return list<string> */
+    public function __sleep(): array
+    {
+        return [
+            ...parent::__sleep(),
+            'mappedBy',
+        ];
+    }
+}

lib/Doctrine/ORM/Mapping/ManyToManyAssociationMapping.php

@@ -4,6 +4,6 @@
 
 namespace Doctrine\ORM\Mapping;
 
-class ManyToManyAssociationMapping extends ToManyAssociationMapping
+interface ManyToManyAssociationMapping extends ToManyAssociationMapping
 {
 }

lib/Doctrine/ORM/Mapping/ManyToManyInverseSideMapping.php

@@ -0,0 +1,9 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Doctrine\ORM\Mapping;
+
+final class ManyToManyInverseSideMapping extends ToManyInverseSideMapping implements ManyToManyAssociationMapping
+{
+}

lib/Doctrine/ORM/Mapping/ManyToManyOwningSideMapping.php

@@ -7,7 +7,7 @@
 use function strtolower;
 use function trim;
 
-final class ManyToManyOwningSideMapping extends ManyToManyAssociationMapping implements AssociationOwningSideMapping
+final class ManyToManyOwningSideMapping extends ToManyOwningSideMapping implements ManyToManyAssociationMapping
 {
     /**
      * Specification of the join table and its join columns (foreign keys).

lib/Doctrine/ORM/Mapping/ManyToOneAssociationMapping.php

@@ -7,26 +7,6 @@
 /**
  * The "many" side of a many-to-one association mapping is always the owning side.
  */
-final class ManyToOneAssociationMapping extends ToOneAssociationMapping implements AssociationOwningSideMapping
+final class ManyToOneAssociationMapping extends ToOneOwningSideMapping
 {
-    /** @var array<string, string> */
-    public array $sourceToTargetKeyColumns = [];
-
-    /** @var array<string, string> */
-    public array $targetToSourceKeyColumns = [];
-
-    /** @var list<JoinColumnMapping> */
-    public array $joinColumns = [];
-
-    /** @return list<string> */
-    public function __sleep(): array
-    {
-        $serialized = parent::__sleep();
-
-        $serialized[] = 'joinColumns';
-        $serialized[] = 'sourceToTargetKeyColumns';
-        $serialized[] = 'targetToSourceKeyColumns';
-
-        return $serialized;
-    }
 }

lib/Doctrine/ORM/Mapping/OneToManyAssociationMapping.php

@@ -4,7 +4,7 @@
 
 namespace Doctrine\ORM\Mapping;
 
-final class OneToManyAssociationMapping extends ToManyAssociationMapping
+final class OneToManyAssociationMapping extends ToManyInverseSideMapping
 {
     /**
      * @param mixed[] $mappingArray

lib/Doctrine/ORM/Mapping/OneToOneAssociationMapping.php

@@ -4,6 +4,6 @@
 
 namespace Doctrine\ORM\Mapping;
 
-class OneToOneAssociationMapping extends ToOneAssociationMapping
+interface OneToOneAssociationMapping extends ToOneAssociationMapping
 {
 }

lib/Doctrine/ORM/Mapping/OneToOneInverseSideMapping.php

@@ -0,0 +1,9 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Doctrine\ORM\Mapping;
+
+final class OneToOneInverseSideMapping extends ToOneInverseSideMapping implements OneToOneAssociationMapping
+{
+}

lib/Doctrine/ORM/Mapping/OneToOneOwningSideMapping.php

@@ -4,26 +4,6 @@
 
 namespace Doctrine\ORM\Mapping;
 
-final class OneToOneOwningSideMapping extends OneToOneAssociationMapping implements AssociationOwningSideMapping
+final class OneToOneOwningSideMapping extends ToOneOwningSideMapping implements OneToOneAssociationMapping
 {
-    /** @var array<string, string> */
-    public array $sourceToTargetKeyColumns = [];
-
-    /** @var array<string, string> */
-    public array $targetToSourceKeyColumns = [];
-
-    /** @var list<JoinColumnMapping> */
-    public array $joinColumns = [];
-
-    /** @return list<string> */
-    public function __sleep(): array
-    {
-        $serialized = parent::__sleep();
-
-        $serialized[] = 'joinColumns';
-        $serialized[] = 'sourceToTargetKeyColumns';
-        $serialized[] = 'targetToSourceKeyColumns';
-
-        return $serialized;
-    }
 }

lib/Doctrine/ORM/Mapping/OwningSideMapping.php

@@ -0,0 +1,28 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Doctrine\ORM\Mapping;
+
+abstract class OwningSideMapping extends AssociationMapping
+{
+    /**
+     * required for bidirectional associations
+     * The name of the field that completes the bidirectional association on
+     * the inverse side. This key must be specified on the owning side of a
+     * bidirectional association.
+     */
+    public string|null $inversedBy = null;
+
+    /** @return list<string> */
+    public function __sleep(): array
+    {
+        $serialized = parent::__sleep();
+
+        if ($this->inversedBy !== null) {
+            $serialized[] = 'inversedBy';
+        }
+
+        return $serialized;
+    }
+}

lib/Doctrine/ORM/Mapping/ToManyAssociationMapping.php

@@ -4,34 +4,6 @@
 
 namespace Doctrine\ORM\Mapping;
 
-abstract class ToManyAssociationMapping extends AssociationMapping
+interface ToManyAssociationMapping
 {
-    /**
-     * Specification of a field on target-entity that is used to index the
-     * collection by. This field HAS to be either the primary key or a unique
-     * column. Otherwise the collection does not contain all the entities that
-     * are actually related.
-     */
-    public string|null $indexBy = null;
-
-    /**
-     * A map of field names (of the target entity) to sorting directions
-     *
-     * @var array<string, 'asc'|'desc'>|null
-     */
-    public array|null $orderBy = null;
-
-    /** @return list<string> */
-    public function __sleep(): array
-    {
-        $serialized = parent::__sleep();
-
-        foreach (['indexBy', 'orderBy'] as $stringOrArrayKey) {
-            if ($this->$stringOrArrayKey !== null) {
-                $serialized[] = $stringOrArrayKey;
-            }
-        }
-
-        return $serialized;
-    }
 }

lib/Doctrine/ORM/Mapping/ToManyAssociationMappingImplementation.php

@@ -0,0 +1,38 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Doctrine\ORM\Mapping;
+
+/** @internal */
+trait ToManyAssociationMappingImplementation
+{
+    /**
+     * Specification of a field on target-entity that is used to index the
+     * collection by. This field HAS to be either the primary key or a unique
+     * column. Otherwise the collection does not contain all the entities that
+     * are actually related.
+     */
+    public string|null $indexBy = null;
+
+    /**
+     * A map of field names (of the target entity) to sorting directions
+     *
+     * @var array<string, 'asc'|'desc'>|null
+     */
+    public array|null $orderBy = null;
+
+    /** @return list<string> */
+    public function __sleep(): array
+    {
+        $serialized = parent::__sleep();
+
+        foreach (['indexBy', 'orderBy'] as $stringOrArrayKey) {
+            if ($this->$stringOrArrayKey !== null) {
+                $serialized[] = $stringOrArrayKey;
+            }
+        }
+
+        return $serialized;
+    }
+}

lib/Doctrine/ORM/Mapping/ToManyInverseSideMapping.php

@@ -0,0 +1,10 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Doctrine\ORM\Mapping;
+
+abstract class ToManyInverseSideMapping extends InverseSideMapping implements ToManyAssociationMapping
+{
+    use ToManyAssociationMappingImplementation;
+}

lib/Doctrine/ORM/Mapping/ToManyOwningSideMapping.php

@@ -0,0 +1,10 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Doctrine\ORM\Mapping;
+
+abstract class ToManyOwningSideMapping extends OwningSideMapping
+{
+    use ToManyAssociationMappingImplementation;
+}