Doctrine\ODM\MongoDB\SchemaManager::doGetDocumentIndexes PHP Method

    private function doGetDocumentIndexes($documentName, array &$visited)
    {
        if (isset($visited[$documentName])) {
            return array();
        }
        $visited[$documentName] = true;
        $class = $this->dm->getClassMetadata($documentName);
        $indexes = $this->prepareIndexes($class);
        $embeddedDocumentIndexes = array();
        // Add indexes from embedded & referenced documents
        foreach ($class->fieldMappings as $fieldMapping) {
            if (isset($fieldMapping['embedded'])) {
                if (isset($fieldMapping['targetDocument'])) {
                    $possibleEmbeds = array($fieldMapping['targetDocument']);
                } elseif (isset($fieldMapping['discriminatorMap'])) {
                    $possibleEmbeds = array_unique($fieldMapping['discriminatorMap']);
                } else {
                    continue;
                }
                foreach ($possibleEmbeds as $embed) {
                    if (isset($embeddedDocumentIndexes[$embed])) {
                        $embeddedIndexes = $embeddedDocumentIndexes[$embed];
                    } else {
                        $embeddedIndexes = $this->doGetDocumentIndexes($embed, $visited);
                        $embeddedDocumentIndexes[$embed] = $embeddedIndexes;
                    }
                    foreach ($embeddedIndexes as $embeddedIndex) {
                        foreach ($embeddedIndex['keys'] as $key => $value) {
                            $embeddedIndex['keys'][$fieldMapping['name'] . '.' . $key] = $value;
                            unset($embeddedIndex['keys'][$key]);
                        }
                        $indexes[] = $embeddedIndex;
                    }
                }
            } elseif (isset($fieldMapping['reference']) && isset($fieldMapping['targetDocument'])) {
                foreach ($indexes as $idx => $index) {
                    $newKeys = array();
                    foreach ($index['keys'] as $key => $v) {
                        if ($key == $fieldMapping['name']) {
                            $key = $fieldMapping['storeAs'] === ClassMetadataInfo::REFERENCE_STORE_AS_ID ? $key : $key . '.$id';
                        }
                        $newKeys[$key] = $v;
                    }
                    $indexes[$idx]['keys'] = $newKeys;
                }
            }
        }
        return $indexes;
    }