$year

Definition

Extracts year using the host calendar.

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

Syntax

{ "$year": <expression> }

Replace angle-bracket placeholders with expressions or values.

Expression supplying the value to process. A field reference such as "$price" reads from the current document.

The value goes directly after the operator name; do not add an input wrapper.

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 input argument:

Input case	Supplied value	Result
null	null	null
missing	Field absent	null
decimal	2.5	Error — Expected a date; convert strings with $toDate
numeric string	"12"	Error — Cannot convert value to date: 12
text	"hello"	Error — Cannot convert value to date: hello
boolean	true	Error — Expected a date; convert strings with $toDate
typed date	{"$date":"2026-01-15T15:00:00Z"}	2026 (int32)
empty array	[]	Error — Expected a date; convert strings with $toDate
numeric array	[1,2,3]	Error — Expected a date; convert strings with $toDate
object	{"x":1}	Error — Expected a date; convert strings with $toDate

Argument handling

Invocation	Result
{"$year":[]}	Error — One date required
{"$year":{"unexpected":1}}	Error — Expected a date; convert strings with $toDate

Examples

Expression:

{
  "$year": {
    "$toDate": "2024-01-02T03:04:05.006Z"
  }
}

Input document:

{}

Observed SrotaX result: 2024 (int32).

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: input

Input case	Supplied value	SrotaX result
null	null	null
missing	Field absent	null
zero	0	Error — Expected a date; convert strings with $toDate
negative	-2	Error — Expected a date; convert strings with $toDate
decimal	2.5	Error — Expected a date; convert strings with $toDate
numeric string	"12"	Error — Cannot convert value to date: 12
text	"hello"	Error — Cannot convert value to date: hello
empty string	""	Error — Cannot convert value to date:
boolean	true	Error — Expected a date; convert strings with $toDate
false	false	Error — Expected a date; convert strings with $toDate
typed date	{"$date":"2026-01-15T15:00:00Z"}	2026 (int32)
decimal128	{"$numberDecimal":"1.25"}	Error — Expected a date; convert strings with $toDate
empty array	[]	Error — Expected a date; convert strings with $toDate
numeric array	[1,2,3]	Error — Expected a date; convert strings with $toDate
mixed array	[1,null,"x",3]	Error — Expected a date; convert strings with $toDate
nested array	[[1,2],[3]]	Error — Expected a date; convert strings with $toDate
empty object	{}	Error — Expected a date; convert strings with $toDate
object	{"x":1}	Error — Expected a date; convert strings with $toDate
ISO date string	"2026-01-15T15:00:00Z"	2026 (int32)

Verification

This page records 22 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: 4 exact BSON matches, 17 both rejected, 1 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.

Show observed differences

Tested case	SrotaX	MongoDB
input / ISO date string	2026 (int32)	Error — Executor error during aggregate command on namespace: fluxion_operator_parity_disposable.$cmd.aggregate :: caused by :: can't convert from BSON type string to Date

Download full comparison evidence.