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$startsWith

Definition

Checks a literal text prefix.

Expression operator · Text · Studio Visual: not exposed. Studio validates the complete expression separately.

Syntax

{ "$startsWith": [ <input>, <text> ] }

Replace angle-bracket placeholders with expressions or values.

Optional parameters may be omitted.

Parameters

Parameter Required Description
input Yes Expression supplying the value to process. A field reference such as "$price" reads from the current document.
text Yes Expression supplying the text value.

Arguments are positional: keep the order shown. The authoring signature accepts 2–2 arguments.

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 Error — Cannot invoke "String.startsWith(String)" because "input" is null
missing Field absent Error — Cannot invoke "String.startsWith(String)" because "input" is null
decimal 2.5 Error — class java.lang.Double cannot be cast to class java.lang.String (java.lang.Double and java.lang.String are in module java.base of loader 'bootstrap')
numeric string "12" false
text "hello" false
boolean true Error — class java.lang.Boolean cannot be cast to class java.lang.String (java.lang.Boolean and java.lang.String are in module java.base of loader 'bootstrap')
typed date {"$date":"2026-01-15T15:00:00Z"} Error — class java.util.Date cannot be cast to class java.lang.String (java.util.Date and java.lang.String are in module java.base of loader 'bootstrap')
empty array [] Error — class java.util.ArrayList cannot be cast to class java.lang.String (java.util.ArrayList and java.lang.String are in module java.base of loader 'bootstrap')
numeric array [1,2,3] Error — class java.util.ArrayList cannot be cast to class java.lang.String (java.util.ArrayList and java.lang.String are in module java.base of loader 'bootstrap')
object {"x":1} Error — class org.bson.Document cannot be cast to class java.lang.String (org.bson.Document is in unnamed module of loader 'app'; java.lang.String is in module java.base of loader 'bootstr

Argument handling

Invocation Result
{"$startsWith":[]} Error — $startsWith expects [string, prefix]
{"$startsWith":{"unexpected":1}} Error — class org.bson.Document cannot be cast to class java.util.List (org.bson.Document is in unnamed module of loader 'app'; java.util.List is in module java.base of loader 'bootstrap')

Examples

Expression: 

{
  "$startsWith": [
    "abc",
    "a"
  ]
}

Input document: 

{}

Observed SrotaX result: true.

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[0]

Input case Supplied value SrotaX result
null null Error — Cannot invoke "String.startsWith(String)" because "input" is null
missing Field absent Error — Cannot invoke "String.startsWith(String)" because "input" is null
zero 0 Error — class java.lang.Integer cannot be cast to class java.lang.String (java.lang.Integer and java.lang.String are in module java.base of loader 'bootstrap')
negative -2 Error — class java.lang.Integer cannot be cast to class java.lang.String (java.lang.Integer and java.lang.String are in module java.base of loader 'bootstrap')
decimal 2.5 Error — class java.lang.Double cannot be cast to class java.lang.String (java.lang.Double and java.lang.String are in module java.base of loader 'bootstrap')
numeric string "12" false
text "hello" false
empty string "" false
boolean true Error — class java.lang.Boolean cannot be cast to class java.lang.String (java.lang.Boolean and java.lang.String are in module java.base of loader 'bootstrap')
false false Error — class java.lang.Boolean cannot be cast to class java.lang.String (java.lang.Boolean and java.lang.String are in module java.base of loader 'bootstrap')
typed date {"$date":"2026-01-15T15:00:00Z"} Error — class java.util.Date cannot be cast to class java.lang.String (java.util.Date and java.lang.String are in module java.base of loader 'bootstrap')
decimal128 {"$numberDecimal":"1.25"} Error — class org.bson.types.Decimal128 cannot be cast to class java.lang.String (org.bson.types.Decimal128 is in unnamed module of loader 'app'; java.lang.String is in module java.base of
empty array [] Error — class java.util.ArrayList cannot be cast to class java.lang.String (java.util.ArrayList and java.lang.String are in module java.base of loader 'bootstrap')
numeric array [1,2,3] Error — class java.util.ArrayList cannot be cast to class java.lang.String (java.util.ArrayList and java.lang.String are in module java.base of loader 'bootstrap')
mixed array [1,null,"x",3] Error — class java.util.ArrayList cannot be cast to class java.lang.String (java.util.ArrayList and java.lang.String are in module java.base of loader 'bootstrap')
nested array [[1,2],[3]] Error — class java.util.ArrayList cannot be cast to class java.lang.String (java.util.ArrayList and java.lang.String are in module java.base of loader 'bootstrap')
empty object {} Error — class org.bson.Document cannot be cast to class java.lang.String (org.bson.Document is in unnamed module of loader 'app'; java.lang.String is in module java.base of loader 'bootstr
object {"x":1} Error — class org.bson.Document cannot be cast to class java.lang.String (org.bson.Document is in unnamed module of loader 'app'; java.lang.String is in module java.base of loader 'bootstr
ISO date string "2026-01-15T15:00:00Z" false

Argument: text[1]

Input case Supplied value SrotaX result
null null Error — Cannot invoke "String.length()" because "prefix" is null
missing Field absent Error — Cannot invoke "String.length()" because "prefix" is null
zero 0 Error — class java.lang.Integer cannot be cast to class java.lang.String (java.lang.Integer and java.lang.String are in module java.base of loader 'bootstrap')
negative -2 Error — class java.lang.Integer cannot be cast to class java.lang.String (java.lang.Integer and java.lang.String are in module java.base of loader 'bootstrap')
decimal 2.5 Error — class java.lang.Double cannot be cast to class java.lang.String (java.lang.Double and java.lang.String are in module java.base of loader 'bootstrap')
numeric string "12" false
text "hello" false
empty string "" true
boolean true Error — class java.lang.Boolean cannot be cast to class java.lang.String (java.lang.Boolean and java.lang.String are in module java.base of loader 'bootstrap')
false false Error — class java.lang.Boolean cannot be cast to class java.lang.String (java.lang.Boolean and java.lang.String are in module java.base of loader 'bootstrap')
typed date {"$date":"2026-01-15T15:00:00Z"} Error — class java.util.Date cannot be cast to class java.lang.String (java.util.Date and java.lang.String are in module java.base of loader 'bootstrap')
decimal128 {"$numberDecimal":"1.25"} Error — class org.bson.types.Decimal128 cannot be cast to class java.lang.String (org.bson.types.Decimal128 is in unnamed module of loader 'app'; java.lang.String is in module java.base of
empty array [] Error — class java.util.ArrayList cannot be cast to class java.lang.String (java.util.ArrayList and java.lang.String are in module java.base of loader 'bootstrap')
numeric array [1,2,3] Error — class java.util.ArrayList cannot be cast to class java.lang.String (java.util.ArrayList and java.lang.String are in module java.base of loader 'bootstrap')
mixed array [1,null,"x",3] Error — class java.util.ArrayList cannot be cast to class java.lang.String (java.util.ArrayList and java.lang.String are in module java.base of loader 'bootstrap')
nested array [[1,2],[3]] Error — class java.util.ArrayList cannot be cast to class java.lang.String (java.util.ArrayList and java.lang.String are in module java.base of loader 'bootstrap')
empty object {} Error — class org.bson.Document cannot be cast to class java.lang.String (org.bson.Document is in unnamed module of loader 'app'; java.lang.String is in module java.base of loader 'bootstr
object {"x":1} Error — class org.bson.Document cannot be cast to class java.lang.String (org.bson.Document is in unnamed module of loader 'app'; java.lang.String is in module java.base of loader 'bootstr
ISO date string "2026-01-15T15:00:00Z" false

Verification

This page records 41 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

This name is a SrotaX extension or belongs to another MongoDB context. It is not compared as a MongoDB aggregation expression. This is not a missing implementation failure.