code: public function decorateClassMetaData(ClassMetadata $c)
      {
          $parentClassName = $c->getName();
  
          if (isset($this->mappings[$parentClassName])) {
              $c->discriminatorMap = array();
              $c->discriminatorMap[strtolower(Str::classname($parentClassName))] = $parentClassName;
              foreach ($this->mappings[$parentClassName] as $className) {
                  $bundlePrefix = Str::infix($this->getBundleName($className), '-');
                  $name = Str::infix(Str::classname(Str::rstrip($className, Str::classname($parentClassName))), '-');
                  $combinedDiscriminator = sprintf('%s-%s', $bundlePrefix, $name);
                  $c->discriminatorMap[$combinedDiscriminator] = $className;
                  $c->subClasses[] = $className;
              }
              $c->subClasses = array_unique($c->subClasses);
          }
      }
docs: Adds the available page types and content item types to the class metadata's discriminatorMap
  
  @param ClassMetadata $c