Doctrine\ODM\MongoDB\Mapping\Driver\AnnotationDriver::addIndex PHP Method

    private function addIndex(ClassMetadataInfo $class, $index, array $keys = array())
    {
        $keys = array_merge($keys, $index->keys);
        $options = array();
        $allowed = array('name', 'dropDups', 'background', 'safe', 'unique', 'sparse', 'expireAfterSeconds');
        foreach ($allowed as $name) {
            if (isset($index->{$name})) {
                $options[$name] = $index->{$name};
            }
        }
        if (!empty($index->partialFilterExpression)) {
            $options['partialFilterExpression'] = $index->partialFilterExpression;
        }
        $options = array_merge($options, $index->options);
        $class->addIndex($keys, $options);
    }