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

    private function addIndex(ClassMetadataInfo $class, \SimpleXmlElement $xmlIndex)
    {
        $attributes = $xmlIndex->attributes();
        $keys = array();
        foreach ($xmlIndex->{'key'} as $key) {
            $keys[(string) $key['name']] = isset($key['order']) ? (string) $key['order'] : 'asc';
        }
        $options = array();
        if (isset($attributes['background'])) {
            $options['background'] = 'true' === (string) $attributes['background'];
        }
        if (isset($attributes['drop-dups'])) {
            $options['dropDups'] = 'true' === (string) $attributes['drop-dups'];
        }
        if (isset($attributes['name'])) {
            $options['name'] = (string) $attributes['name'];
        }
        if (isset($attributes['safe'])) {
            $options['safe'] = 'true' === (string) $attributes['safe'];
        }
        if (isset($attributes['sparse'])) {
            $options['sparse'] = 'true' === (string) $attributes['sparse'];
        }
        if (isset($attributes['unique'])) {
            $options['unique'] = 'true' === (string) $attributes['unique'];
        }
        if (isset($xmlIndex->{'option'})) {
            foreach ($xmlIndex->{'option'} as $option) {
                $value = (string) $option['value'];
                if ($value === 'true') {
                    $value = true;
                } elseif ($value === 'false') {
                    $value = false;
                } elseif (is_numeric($value)) {
                    $value = preg_match('/^[-]?\\d+$/', $value) ? (int) $value : (double) $value;
                }
                $options[(string) $option['name']] = $value;
            }
        }
        if (isset($xmlIndex->{'partial-filter-expression'})) {
            $partialFilterExpressionMapping = $xmlIndex->{'partial-filter-expression'};
            if (isset($partialFilterExpressionMapping->and)) {
                foreach ($partialFilterExpressionMapping->and as $and) {
                    if (!isset($and->field)) {
                        continue;
                    }
                    $partialFilterExpression = $this->getPartialFilterExpression($and->field);
                    if (!$partialFilterExpression) {
                        continue;
                    }
                    $options['partialFilterExpression']['$and'][] = $partialFilterExpression;
                }
            } elseif (isset($partialFilterExpressionMapping->field)) {
                $partialFilterExpression = $this->getPartialFilterExpression($partialFilterExpressionMapping->field);
                if ($partialFilterExpression) {
                    $options['partialFilterExpression'] = $partialFilterExpression;
                }
            }
        }
        $class->addIndex($keys, $options);
    }