bytebase/bytebase · error

cannot get index key from index info

Error message

cannot get index key from index info

What it means

getIndexes reads the "key" field of each index document — the key specification (e.g. {field: 1, other: -1}) — from the decoded bson.M. This error is thrown when the index document lacks a "key" field entirely. Every MongoDB index document must contain a key spec, so its absence means the server returned malformed index metadata.

Source

Thrown at backend/plugin/db/mongodb/sync.go:220

	}
	indexMap := make(map[string]*storepb.IndexMetadata)
	defer indexCursor.Close(ctx)
	for indexCursor.Next(ctx) {
		var indexInfo bson.M
		if err := indexCursor.Decode(&indexInfo); err != nil {
			return nil, errors.Wrap(err, "failed to decode index info")
		}
		name, ok := indexInfo["name"]
		if !ok {
			return nil, errors.New("cannot get index name from index info")
		}
		indexName, ok := name.(string)
		if !ok {
			return nil, errors.New("cannot cinvert index name to string")
		}
		key, ok := indexInfo["key"]
		if !ok {
			return nil, errors.New("cannot get index key from index info")
		}
		expression, err := json.Marshal(key)
		if err != nil {
			return nil, errors.Wrap(err, "cannot marshal index key to json")
		}
		unique := false
		if u, ok := indexInfo["unique"]; ok {
			unique, ok = u.(bool)
			if !ok {
				return nil, errors.New("cannot convert unique to bool")
			}
		}

		if _, ok := indexMap[indexName]; !ok {
			indexMap[indexName] = &storepb.IndexMetadata{
				Name:   indexName,
				Unique: unique,
			}

View on GitHub (pinned to 1870550677)

Solutions

1. Run db.collection.getIndexes() and confirm every returned document contains a key field
2. Drop and rebuild malformed indexes on the affected collection if the server catalog is corrupted
3. Verify the target service fully implements the listIndexes contract; if using a proxy or emulation layer, test against real MongoDB to isolate it
4. Log the offending index document and skip it with a warning instead of failing the full sync

Example fix

// before
key, ok := indexInfo["key"]
if !ok {
	return nil, errors.New("cannot get index key from index info")
}
// after
key, ok := indexInfo["key"]
if !ok {
	slog.Warn("index info missing key spec", slog.Any("indexName", indexName))
	continue
}

cur, _ := db.Collection(coll).Indexes().List(ctx)
for cur.Next(ctx) {
	var info bson.M
	cur.Decode(&info)
	if _, ok := info["key"]; !ok {
		return fmt.Errorf("index %v missing key spec", info["name"])
	}
}

func indexHasKey(info bson.M) (bson.M, bool) {
	key, ok := info["key"].(bson.M)
	return key, ok
}

if err := driver.SyncDBSchema(ctx); err != nil {
	if strings.Contains(err.Error(), "cannot get index key from index info") {
		// log offending index document and skip the collection
		return nil
	}
	return err
}

When it happens

Trigger: SyncDBSchema → getIndexes: a listIndexes document has a name but no "key" field, typically from a compatibility layer, a mock, or a corrupted catalog entry.

Common situations: DocumentDB/FerretDB or proxy endpoints emitting incomplete index documents; hand-written test fixtures missing the key field; corrupted index catalog entries after failed builds.

Related errors

• cannot convert collection name to string
• cannot get size from collStats command result
• cannot get index name from index info
• cannot cinvert index name to string
• cannot convert unique to bool

AI-assisted analysis of bytebase/bytebase@1870550677 (2026-09-06). Data as JSON: /api/errors/257b33facbf3792a. Report an issue: GitHub.