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$dateToString

Definition

Formats a typed date using supported numeric format tokens.

Expression operator · Dates · Studio Visual: available. Studio validates the complete expression separately.

Syntax

{
  "$dateToString": {
    "date": <date>,
    "format": <format>,
    "timezone": <timezone>,
    "onNull": <onNull>
  }
}

Replace angle-bracket placeholders with expressions or values.

Optional parameters may be omitted.

Parameters

Parameter Required Description
date Yes Expression supplying the date to process.
format No Date format string. See Supported values below for the tokens implemented by this operator. Default: %Y-%m-%dT%H:%M:%S.%LZ for UTC, or %Y-%m-%dT%H:%M:%S.%L for a non-UTC zone.
timezone No Timezone name or offset used for the calendar operation, for example "America/Toronto" or "+05:30". Defaults to UTC when omitted.
onNull No Fallback expression for null or missing input. If omitted, the null-input result is null.

Supported values

Supported format tokens: %Y, %m, %d, %H, %M, %S, %L, %j, %G, %V, %u, %z, %%, %w, %U, %Z. Unsupported tokens raise an error. For example, %Y-%m-%d represents year-month-day.

Behavior

The following observations use the example expression below. Each row substitutes one argument while retaining the other example arguments. A missing field differs from an explicit null; the result shown is what Core actually returned.

Date cases use JVM timezone America/Toronto and locale en-IN. Named date operators with timezone support generally default to UTC; older single-date extraction operators can use the JVM timezone.

For the date argument:

Input case Supplied value Result
null null null
missing Field absent null
decimal 2.5 Error — $dateToString date must be a date, timestamp, or ObjectId; convert strings using $toDate
numeric string "12" Error — $dateToString date must be a date, timestamp, or ObjectId; convert strings using $toDate
text "hello" Error — $dateToString date must be a date, timestamp, or ObjectId; convert strings using $toDate
boolean true Error — $dateToString date must be a date, timestamp, or ObjectId; convert strings using $toDate
typed date {"$date":"2026-01-15T15:00:00Z"} "2026-01-15"
empty array [] Error — $dateToString date must be a date, timestamp, or ObjectId; convert strings using $toDate
numeric array [1,2,3] Error — $dateToString date must be a date, timestamp, or ObjectId; convert strings using $toDate
object {"x":1} Error — $dateToString date must be a date, timestamp, or ObjectId; convert strings using $toDate

Argument handling

Invocation Result
{"$dateToString":[]} Error — $dateToString requires date
{"$dateToString":{"unexpected":1}} Error — $dateToString requires date

Examples

Expression: 

{
  "$dateToString": {
    "date": {
      "$toDate": "2024-01-02T03:04:05.006Z"
    },
    "format": "%Y-%m-%d",
    "timezone": "UTC"
  }
}

Input document: 

{}

Observed SrotaX result: "2024-01-02".

Detailed input cases

Expand the complete argument-by-argument test matrix

Each table changes only the indicated argument from the example above. Other arguments retain their baseline values. Values normally come from the input field probe; literal configuration arguments are replaced directly. “Missing” means the field is absent, not explicitly null. Numeric strings are strings, not numbers.

Argument: date

Input case Supplied value SrotaX result
null null null
missing Field absent null
zero 0 Error — $dateToString date must be a date, timestamp, or ObjectId; convert strings using $toDate
negative -2 Error — $dateToString date must be a date, timestamp, or ObjectId; convert strings using $toDate
decimal 2.5 Error — $dateToString date must be a date, timestamp, or ObjectId; convert strings using $toDate
numeric string "12" Error — $dateToString date must be a date, timestamp, or ObjectId; convert strings using $toDate
text "hello" Error — $dateToString date must be a date, timestamp, or ObjectId; convert strings using $toDate
empty string "" Error — $dateToString date must be a date, timestamp, or ObjectId; convert strings using $toDate
boolean true Error — $dateToString date must be a date, timestamp, or ObjectId; convert strings using $toDate
false false Error — $dateToString date must be a date, timestamp, or ObjectId; convert strings using $toDate
typed date {"$date":"2026-01-15T15:00:00Z"} "2026-01-15"
decimal128 {"$numberDecimal":"1.25"} Error — $dateToString date must be a date, timestamp, or ObjectId; convert strings using $toDate
empty array [] Error — $dateToString date must be a date, timestamp, or ObjectId; convert strings using $toDate
numeric array [1,2,3] Error — $dateToString date must be a date, timestamp, or ObjectId; convert strings using $toDate
mixed array [1,null,"x",3] Error — $dateToString date must be a date, timestamp, or ObjectId; convert strings using $toDate
nested array [[1,2],[3]] Error — $dateToString date must be a date, timestamp, or ObjectId; convert strings using $toDate
empty object {} Error — $dateToString date must be a date, timestamp, or ObjectId; convert strings using $toDate
object {"x":1} Error — $dateToString date must be a date, timestamp, or ObjectId; convert strings using $toDate
ISO date string "2026-01-15T15:00:00Z" Error — $dateToString date must be a date, timestamp, or ObjectId; convert strings using $toDate
omitted named argument Argument removed Error — $dateToString requires date

Argument: format

Input case Supplied value SrotaX result
null null null
missing Field absent null
zero 0 Error — $dateToString format must be a string
negative -2 Error — $dateToString format must be a string
decimal 2.5 Error — $dateToString format must be a string
numeric string "12" "12"
text "hello" "hello"
empty string "" ""
boolean true Error — $dateToString format must be a string
false false Error — $dateToString format must be a string
typed date {"$date":"2026-01-15T15:00:00Z"} Error — $dateToString format must be a string
decimal128 {"$numberDecimal":"1.25"} Error — $dateToString format must be a string
empty array [] Error — $dateToString format must be a string
numeric array [1,2,3] Error — $dateToString format must be a string
mixed array [1,null,"x",3] Error — $dateToString format must be a string
nested array [[1,2],[3]] Error — $dateToString format must be a string
empty object {} Error — $dateToString format must be a string
object {"x":1} Error — $dateToString format must be a string
ISO date string "2026-01-15T15:00:00Z" "2026-01-15T15:00:00Z"
omitted named argument Argument removed "2024-01-02T03:04:05.006Z"

Argument: timezone

Input case Supplied value SrotaX result
null null null
missing Field absent null
zero 0 Error — $dateToString timezone must be a string
negative -2 Error — $dateToString timezone must be a string
decimal 2.5 Error — $dateToString timezone must be a string
numeric string "12" Error — Invalid ID for region-based ZoneId, invalid format: 12
text "hello" Error — Unknown time-zone ID: hello
empty string "" Error — Invalid ID for ZoneOffset, invalid format:
boolean true Error — $dateToString timezone must be a string
false false Error — $dateToString timezone must be a string
typed date {"$date":"2026-01-15T15:00:00Z"} Error — $dateToString timezone must be a string
decimal128 {"$numberDecimal":"1.25"} Error — $dateToString timezone must be a string
empty array [] Error — $dateToString timezone must be a string
numeric array [1,2,3] Error — $dateToString timezone must be a string
mixed array [1,null,"x",3] Error — $dateToString timezone must be a string
nested array [[1,2],[3]] Error — $dateToString timezone must be a string
empty object {} Error — $dateToString timezone must be a string
object {"x":1} Error — $dateToString timezone must be a string
ISO date string "2026-01-15T15:00:00Z" Error — Invalid ID for region-based ZoneId, invalid format: 2026-01-15T15:00:00Z
omitted named argument Argument removed "2024-01-02"

Argument: onNull

Input case Supplied value SrotaX result
null null "2024-01-02"
missing Field absent "2024-01-02"
zero 0 "2024-01-02"
negative -2 "2024-01-02"
decimal 2.5 "2024-01-02"
numeric string "12" "2024-01-02"
text "hello" "2024-01-02"
empty string "" "2024-01-02"
boolean true "2024-01-02"
false false "2024-01-02"
typed date {"$date":"2026-01-15T15:00:00Z"} "2024-01-02"
decimal128 {"$numberDecimal":"1.25"} "2024-01-02"
empty array [] "2024-01-02"
numeric array [1,2,3] "2024-01-02"
mixed array [1,null,"x",3] "2024-01-02"
nested array [[1,2],[3]] "2024-01-02"
empty object {} "2024-01-02"
object {"x":1} "2024-01-02"
ISO date string "2026-01-15T15:00:00Z" "2024-01-02"
omitted named argument Argument removed "2024-01-02"

Verification

This page records 83 executed cases. It covers individual argument substitutions, not every cross-product of arguments, locale, daylight-saving transitions, numeric overflow, collation or resource limits. No untested behavior is guaranteed.

Download exact expressions, inputs and SrotaX results. Errors are observed messages, not stable public error codes. The reference generator reads the checked-in execution report; do not edit generated observations by hand.

MongoDB differences

Compared with MongoDB 9.0.4: 34 exact BSON matches, 49 both rejected, 0 value/type/acceptance differences, 0 object-field-order differences.

“Exact” includes numeric BSON types and object key order. A value of 3 as int32 differs from 3.0 as double. Object-field-order differences are reported separately; object key ordering is not enforced by the engine regression baseline. Both rejected does not mean the error codes or messages match. This is finite-case evidence, not full compatibility certification.

No differences were observed in the compared cases.

Download full comparison evidence.