Fix crash when accessing out of bounds index of a collection (realm#4416

)

* Fix crash when accessing out of bounds index of a collection

Collection will now return `undefined` for out of bound indexes.
Added a test to cover this.

packages/realm-react/CHANGELOG.md

@@ -1,3 +1,17 @@
+x.x.x Release notes (yyyy-MM-dd)
+=============================================================
+### Enhancements
+* None.
+
+### Fixed
+* Fixed bug when trying to access a collection result with an out of bounds index.
+
+### Compatibility
+* None
+
+### Internal
+* None
+
 0.2.0 Release notes (2022-03-07)
 =============================================================
 ### Enhancements

packages/realm-react/src/__tests__/useQueryHook.test.tsx

@@ -67,7 +67,7 @@ const testDataSet = [
  { _id: 6, name: "Sadie", color: "gold", gender: "female", age: 5 },
 ];
 
-describe("useQuery", () => {
+describe("useQueryHook", () => {
  beforeEach(() => {
  const realm = new Realm(configuration);
  realm.write(() => {
@@ -101,4 +101,10 @@ describe("useQuery", () => {
  expect(collection.length).toBe(6);
  expect(collection[0]).toEqual(collection?.[0]);
  });
+ it("should return undefined indexes that are out of bounds", () => {
+ const { result } = renderHook(() => useQuery<IDog>("dog"));
+ const collection = result.current;
+
+ expect(collection[99]).toBe(undefined);
+ });
 });

packages/realm-react/src/cachedCollection.ts

@@ -24,8 +24,8 @@ function getCacheKey(id: string) {
 }
 
 /**
-  * Arguments object for {@link cachedCollection}.
-  */
+ * Arguments object for {@link cachedCollection}.
+ */
 type CachedCollectionArgs<T> = {
  /**
  * The {@link Realm.Collection} to proxy
@@ -40,7 +40,7 @@ type CachedCollectionArgs<T> = {
  * (derived) version of the collection to reuse the same cache, preventing excess new object
  * references being created.
  */
- collectionCache?: Map<string, T>;
+ objectCache?: Map<string, T>;
  /**
  * Optional flag specifying that this is a derived (`sorted` or `filtered`) version of
  * an existing collection, so we should not create or remove listeners or clear the cache
@@ -66,12 +66,7 @@ export function createCachedCollection<T extends Realm.Object>({
  updateCallback,
  objectCache = new Map(),
  isDerived = false,
-}: {
- collection: Realm.Collection<T>;
- updateCallback: () => void;
- objectCache?: Map<string, T>;
- isDerived?: boolean;
-}): { collection: Realm.Collection<T>; tearDown: () => void } {
+}: CachedCollectionArgs<T>): { collection: Realm.Collection<T>; tearDown: () => void } {
  const cachedCollectionHandler: ProxyHandler<Realm.Collection<T & Realm.Object>> = {
  get: function (target, key) {
  // Pass functions through
@@ -100,6 +95,17 @@ export function createCachedCollection<T extends Realm.Object>({
  // If the key is numeric, check if we have a cached object for this key
  const index = Number(key);
  const object = target[index];
+
+ // If the collection is modeled in a way that objects can be null
+ // then we should return null instead of undefined to stay semantically
+ // correct
+ if (object === null) {
+ return null;
+ } else if (typeof object === "undefined") {
+ // If there is no object at this index, return undefined
+ return undefined;
+ }
+
  const objectId = object._objectId();
  const cacheKey = getCacheKey(objectId);