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

…criminator. (#8378)

lib/Doctrine/ORM/Tools/SchemaValidator.php

@@ -26,6 +26,7 @@
 
 use function array_diff;
 use function array_key_exists;
+use function array_search;
 use function array_values;
 use function class_exists;
 use function class_parents;
@@ -255,6 +256,12 @@ 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 " .