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$toUpper

Definition

Converts text to upper case.

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

Syntax

{ "$toUpper": <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.

For the input argument:

Input case Supplied value Result
null null ""
missing Field absent ""
decimal 2.5 Error — $toUpper requires a string.
numeric string "12" "12"
text "hello" "HELLO"
boolean true Error — $toUpper requires a string.
typed date {"$date":"2026-01-15T15:00:00Z"} Error — $toUpper requires a string.
empty array [] Error — $toUpper requires a string.
numeric array [1,2,3] Error — $toUpper requires a string.
object {"x":1} Error — $toUpper requires a string.

Argument handling

Invocation Result
{"$toUpper":[]} Error — $toUpper requires one argument
{"$toUpper":{"unexpected":1}} Error — $toUpper requires a string.

Examples

Expression: 

{
  "$toUpper": "Ca"
}

Input document: 

{}

Observed SrotaX result: "CA".

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 ""
missing Field absent ""
zero 0 Error — $toUpper requires a string.
negative -2 Error — $toUpper requires a string.
decimal 2.5 Error — $toUpper requires a string.
numeric string "12" "12"
text "hello" "HELLO"
empty string "" ""
boolean true Error — $toUpper requires a string.
false false Error — $toUpper requires a string.
typed date {"$date":"2026-01-15T15:00:00Z"} Error — $toUpper requires a string.
decimal128 {"$numberDecimal":"1.25"} Error — $toUpper requires a string.
empty array [] Error — $toUpper requires a string.
numeric array [1,2,3] Error — $toUpper requires a string.
mixed array [1,null,"x",3] Error — $toUpper requires a string.
nested array [[1,2],[3]] Error — $toUpper requires a string.
empty object {} Error — $toUpper requires a string.
object {"x":1} Error — $toUpper requires a string.
ISO date string "2026-01-15T15:00:00Z" "2026-01-15T15:00:00Z"

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: 7 exact BSON matches, 10 both rejected, 5 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 / zero Error — $toUpper requires a string. "0"
input / negative Error — $toUpper requires a string. "-2"
input / decimal Error — $toUpper requires a string. "2.5"
input / typed date Error — $toUpper requires a string. "2026-01-15T15:00:00.000Z"
input / decimal128 Error — $toUpper requires a string. "1.25"

Download full comparison evidence.