private function getPersistersNode()
    {
        $node = $this->createRootNode('persisters');
        return $node
            ->isRequired()
            ->useAttributeAsKey('name')
            ->prototype('array')
                ->children()

                    ->enumNode('type')
                        ->values(['mongodb', null])
                    ->end()
                    ->scalarNode('service')->cannotBeEmpty()->end()

                    ->arrayNode('parameters')
                        ->performNoDeepMerging()
                        ->prototype('variable')->end()
                    ->end()
                ->end()
            ->end()
            ->validate()
                ->always(function($v) {
                    $this->validatePersisters($v);
                    return $v;
                })
            ->end()
        ;
    }