[GH-6578] Add validation that inherited entity class is mapped in dis…

…criminator.

lib/Doctrine/ORM/Tools/SchemaValidator.php

@@ -22,6 +22,8 @@
 use Doctrine\ORM\EntityManagerInterface;
 use Doctrine\ORM\Mapping\ClassMetadataInfo;
 use Doctrine\DBAL\Types\Type;
+
+use function array_search;
 use function count;
 
 /**
@@ -256,6 +258,12 @@ public function validateClass(ClassMetadataInfo $class)
             }
         }
 
+        if (! $class->isInheritanceTypeNone() && ! $class->isRootEntity() && array_search($class->name, $class->discriminatorMap) === false) {
+            $ce[] = "Entity class '" . $class->name . "' is part of inheritance hierarchy, but is " .
+                "not mapped in the root entity '" . $class->rootEntityName . "' discriminator map. " .
+                'All subclasses must be listed in the discriminator map.';
+        }
+
         foreach ($class->subClasses as $subClass) {
             if (!in_array($class->name, class_parents($subClass))) {
                 $ce[] = "According to the discriminator map class '" . $subClass . "' has to be a child ".