What causes "failed to scan comment: %w" in gastownhall/beads?

failed to scan comment: %w

Error message

failed to scan comment: %w

What it means

scanComments fails when a comment row cannot be scanned into types.Comment — the result set's columns don't match the scan destinations (ID, IssueID, Author, Text, CreatedAt). Typically caused by NULLs in non-nullable fields or a column type/count mismatch after schema changes. The raw sql error is wrapped for inspection.

Source

Thrown at internal/storage/dolt/events.go:185

// GetCommentCounts returns the number of comments for each issue in a single batch query.
// Delegates to issueops.GetCommentCountsInTx for shared query logic.
func (s *DoltStore) GetCommentCounts(ctx context.Context, issueIDs []string) (map[string]int, error) {
	var result map[string]int
	err := s.withReadTx(ctx, func(tx *sql.Tx) error {
		var err error
		result, err = issueops.GetCommentCountsInTx(ctx, tx, issueIDs)
		return err
	})
	return result, err
}

// scanComments scans comment rows into a slice.
func scanComments(rows *sql.Rows) ([]*types.Comment, error) {
	var comments []*types.Comment
	for rows.Next() {
		var c types.Comment
		if err := rows.Scan(&c.ID, &c.IssueID, &c.Author, &c.Text, &c.CreatedAt); err != nil {
			return nil, fmt.Errorf("failed to scan comment: %w", err)
		}
		comments = append(comments, &c)
	}
	return comments, rows.Err()
}

View on GitHub (pinned to 71377f2769)

Solutions

Find the offending row(s) via SQL (`SELECT * FROM comments WHERE author IS NULL OR text IS NULL OR created_at IS NULL`) and fix or delete them.
If you altered the comments table, restore the expected schema (column names, order, types, NOT NULL constraints).
Run any pending migrations (`bd doctor` / migrate) so the schema matches the code's expectations.
As a last resort, export good data, recreate the table with the canonical schema, and re-import.

Example fix

// before: manual insert leaving NULLs
INSERT INTO comments (id, issue_id, text) VALUES ('c1', 'bd-1', 'hi');
// after: supply all non-nullable columns
INSERT INTO comments (id, issue_id, author, text, created_at)
VALUES ('c1', 'bd-1', 'alice', 'hi', NOW());

Defensive patterns

Strategy: validation

Validate before calling

// SQL: detect rows that will fail the scan before reading via bd
SELECT id FROM comments
WHERE author IS NULL OR text IS NULL OR created_at IS NULL OR issue_id IS NULL;

Type guard

func IsCommentScanError(err error) bool {
	return err != nil && strings.Contains(err.Error(), "failed to scan comment")
}

Try / catch

comments, err := store.GetIssueComments(ctx, issueID)
if err != nil && strings.Contains(err.Error(), "failed to scan comment") {
	return fmt.Errorf("corrupt comment row; fix NULLs in comments table: %w", err)
}

Prevention

Never insert comment rows manually without all required columns.
Enforce NOT NULL constraints in the comments schema and rely on them.
Validate schema after restores/backups before normal use.
Use nullable Go scan types if a column is legitimately optional.

When it happens

Trigger: A comment row has NULL author, text, or created_at (e.g. inserted manually via dolt sql); the comments table was altered so column order/types differ; a schema migration left mixed-format rows.

Common situations: Hand-editing the database with `dolt sql` and omitting required fields; upgrading bd across versions where the Comment struct gained fields the old schema can't satisfy; restoring a partial backup missing some columns.

Related errors

AI-assisted analysis of gastownhall/beads@71377f2769 (2026-08-30). Data as JSON: /api/errors/be2a1d506da7fd8a. Report an issue: GitHub.