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Fix MongoDB parity: regex members of $in/$nin pattern-match strings, empty $elemMatch matches document elements #11

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Merged
pubkey merged 1 commit into from
Jul 23, 2026
Merged

Fix MongoDB parity: regex members of $in/$nin pattern-match strings, empty $elemMatch matches document elements #11

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16 changes: 15 additions & 1 deletion src/operators/_predicates.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -38,6 +38,11 @@ type ConversionType = number | Exclude<JsType, "function"> | BsonType;
* This includes pre-compiling the query and determining if we need to wrap non-objects in a temporary object.
*/
function elemMatchPredicate(criteria: AnyObject, options: Options) {
// MongoDB parity: an empty $elemMatch matches arrays that contain
// at least one document (object) element.
if (Object.keys(criteria).length === 0) {
return (v: Any) => isObject(v);
}
// precompute criteria and format function at query compilation time
let format = (x: Any) => x;
// determine if we need to wrap the criteria in a temporary key to avoid confusion with top-level operators.
Expand Down Expand Up @@ -125,7 +130,16 @@ export function $ne(a: Any, b: Any, options?: Options): boolean {
export function $in(a: Any[], b: Any[], _options?: Options): boolean {
// queries for null should be able to find undefined fields
if (isNil(a)) return b.some(v => v === null);
return intersection([ensureArray(a), b]).length > 0;
const values = ensureArray(a);
if (intersection([values, b]).length > 0) return true;
// MongoDB parity: a regular expression in the query array matches
// string values as a pattern, in addition to equal regex values.
// https://docs.mongodb.com/manual/reference/operator/query/in/
const patterns = b.filter(isRegExp) as RegExp[];
return (
patterns.length > 0 &&
values.some(v => isString(v) && patterns.some(re => re.test(v)))
);
}

/**
Expand Down