$toDate (Convert to Date)

Last updated: 2026-10-09

$toDate (Convert to Date)

$toDate converts a value to a BSON Date. It passes dates through, treats numbers as millisecond timestamps, and parses ISO 8601 strings. Typical uses: converting log time strings into dates for day-level grouping or standardizing millisecond timestamps from frontends. Invalid strings throw, so prefer $convert with onError for dirty data. Null input yields null. Compared with $dateFromString, $toDate has simpler syntax and auto-detects ISO formats.

📝 Syntax

{ $toDate: <expression> }

⚙️ Parameters

Returns：A Date; null when the input is null

▶ Example

Run the commands below in your local mongosh (requires a running mongod):

// $toDate: parse a time string into a date
db.logs.aggregate([
  { $project: {
      ts: { $toDate: '$timeStr' }
  } }
])

Output：

{ '_id': 1, 'ts': { '$date': '2026-09-25T08:00:00Z' } }

📌 Notes

• Numbers are millisecond timestamps; second-level timestamps need a multiply by 1000 first
• Non-ISO strings (e.g. '2026/09/25') throw
• null input yields null

🏷️ Related Tags

💡 Related Cases

📚 Related Tutorials

❓ FAQ

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